Correct the version detection of erlangplugins

We weren't correctly identifying the erlang version.  Instead we were detecting the erts version.

Old result:
```javascript
    "erlang": {
      "version": "7.3",
      "options": [
        "SMP",
        "ASYNC_THREADS",
        "HIPE"
      ],
      "emulator": "BEAM"
    },
```

New result
```javascript
    "erlang": {
      "version": "18",
      "erts_version": "7.3",
      "nif_version": "2.10",
      "options": [
        "SMP",
        "ASYNC_THREADS",
        "HIPE"
      ],
      "emulator": "BEAM"
    },
```

2 files changed, 60 insertions, 37 deletions

diff --git a/lib/ohai/plugins/erlang.rb b/lib/ohai/plugins/erlang.rb
index fc947bee..93295ee7 100644
--- a/lib/ohai/plugins/erlang.rb
+++ b/lib/ohai/plugins/erlang.rb
@@ -18,26 +18,43 @@
 
 Ohai.plugin(:Erlang) do
   provides "languages/erlang"
-
   depends "languages"
 
   collect_data do
-    output = nil
+    begin
+      so = shell_out("erl -eval 'erlang:display(erlang:system_info(otp_release)), erlang:display(erlang:system_info(version)), erlang:display(erlang:system_info(nif_version)), halt().'  -noshell")
+      # Sample output:
+      # "18"
+      # "7.3"
+      # "2.10"
+      if so.exitstatus == 0
+        erlang = Mash.new
+        output = so.stdout.split(/\r\n/).map! { |x| x.delete('\\"') }
+        erlang[:version] = output[0]
+        erlang[:erts_version] = output[1]
+        erlang[:nif_version] = output[2]
+      end
+    rescue Ohai::Exceptions::Exec
+      Ohai::Log.debug('Erlang plugin: Could not shell_out "erl -eval \'erlang:display(erlang:system_info(otp_release)), erlang:display(erlang:system_info(version)), erlang:display(erlang:system_info(nif_version)), halt().\'  -noshell". Skipping plugin')
+    end
 
-    erlang = Mash.new
-    so = shell_out("erl +V")
-    if so.exitstatus == 0
-      output = so.stderr.split
-      if output.length >= 6
-        options = output[1]
-        options.gsub!(/(\(|\))/, "")
-        erlang[:version] = output[5]
-        erlang[:options] = options.split(",")
-        erlang[:emulator] = output[2].gsub!(/(\(|\))/, "")
-        if erlang[:version] && erlang[:options] && erlang[:emulator]
-          languages[:erlang] = erlang
+    begin
+      so = shell_out("erl +V")
+      # Sample output:
+      # Erlang (SMP,ASYNC_THREADS,HIPE) (BEAM) emulator version 7.3
+      if so.exitstatus == 0
+        output = so.stderr.split
+        if output.length >= 6
+          options = output[1]
+          options.gsub!(/(\(|\))/, "")
+          erlang[:options] = options.split(",")
+          erlang[:emulator] = output[2].gsub!(/(\(|\))/, "")
         end
       end
+    rescue Ohai::Exceptions::Exec
+      Ohai::Log.debug('Erlang plugin: Could not shell_out "erl +V". Skipping plugin')
     end
+
+    languages[:erlang] = erlang unless erlang.empty?
   end
 end
diff --git a/spec/unit/plugins/erlang_spec.rb b/spec/unit/plugins/erlang_spec.rb
index cdb0a340..0f407b69 100644
--- a/spec/unit/plugins/erlang_spec.rb
+++ b/spec/unit/plugins/erlang_spec.rb
@@ -20,41 +20,47 @@
 require File.expand_path(File.dirname(__FILE__) + "/../../spec_helper.rb")
 
 describe Ohai::System, "plugin erlang" do
+  let(:plugin) { get_plugin("erlang") }
 
   before(:each) do
-    @plugin = get_plugin("erlang")
-    @plugin[:languages] = Mash.new
-    @stderr = "Erlang (ASYNC_THREADS,SMP,HIPE) (BEAM) emulator version 5.6.2\n"
-    allow(@plugin).to receive(:shell_out).with("erl +V").and_return(mock_shell_out(0, "", @stderr))
+    plugin[:languages] = Mash.new
+    erl_v_output = "Erlang (SMP,ASYNC_THREADS,HIPE) (BEAM) emulator version 7.3\n"
+    erl_systeminfo_output = "\"18\"\r\n\"7.3\"\r\n\"2.10\"\r\n"
+    allow(plugin).to receive(:shell_out).with("erl +V")
+                                        .and_return(mock_shell_out(0, "", erl_v_output))
+    allow(plugin).to receive(:shell_out).with("erl -eval 'erlang:display(erlang:system_info(otp_release)), erlang:display(erlang:system_info(version)), erlang:display(erlang:system_info(nif_version)), halt().'  -noshell")
+                                        .and_return(mock_shell_out(0, erl_systeminfo_output, ""))
   end
 
-  it "should get the erlang version from erl +V" do
-    expect(@plugin).to receive(:shell_out).with("erl +V").and_return(mock_shell_out(0, "", @stderr))
-    @plugin.run
+  it "sets languages[:erlang][:options]" do
+    plugin.run
+    expect(plugin.languages[:erlang][:options]).to eql(%w{SMP ASYNC_THREADS HIPE})
   end
 
-  it "should set languages[:erlang][:version]" do
-    @plugin.run
-    expect(@plugin.languages[:erlang][:version]).to eql("5.6.2")
+  it "sets languages[:erlang][:emulator]" do
+    plugin.run
+    expect(plugin.languages[:erlang][:emulator]).to eql("BEAM")
   end
 
-  it "should set languages[:erlang][:options]" do
-    @plugin.run
-    expect(@plugin.languages[:erlang][:options]).to eql(%w{ASYNC_THREADS SMP HIPE})
+  it "sets languages[:erlang][:version]" do
+    plugin.run
+    expect(plugin.languages[:erlang][:version]).to eql("18")
   end
 
-  it "should set languages[:erlang][:emulator]" do
-    @plugin.run
-    expect(@plugin.languages[:erlang][:emulator]).to eql("BEAM")
+  it "sets languages[:erlang][:erts_version]" do
+    plugin.run
+    expect(plugin.languages[:erlang][:erts_version]).to eql("7.3")
   end
 
-  it "should not set the languages[:erlang] tree up if erlang command fails" do
-    @status = 1
-    @stdin = ""
-    @stderr = "Erlang (ASYNC_THREADS,SMP,HIPE) (BEAM) emulator version 5.6.2\n"
-    allow(@plugin).to receive(:shell_out).with("erl +V").and_return(mock_shell_out(1, "", @stderr))
-    @plugin.run
-    expect(@plugin.languages).not_to have_key(:erlang)
+  it "sets languages[:erlang][:nif_version]" do
+    plugin.run
+    expect(plugin.languages[:erlang][:nif_version]).to eql("2.10")
+  end
+
+  it "does not set languages[:erlang] if the erl commands fails" do
+    allow(plugin).to receive(:shell_out).and_raise(Ohai::Exceptions::Exec)
+    plugin.run
+    expect(plugin.languages).not_to have_key(:erlang)
   end
 
 end