Add rbenv pluginrbenv

This gives us information on the available ruby versions in rbenv

```javascript
  "rbenv": {
    "default": "2.4.1",
    "versions": [
      "2.4.1"
    ],
    "rbenv_version": "1.1.1"
  }
```

Signed-off-by: Tim Smith <tsmith@chef.io>

2 files changed, 114 insertions, 0 deletions

diff --git a/lib/ohai/plugins/rbenv.rb b/lib/ohai/plugins/rbenv.rb
new file mode 100644
index 00000000..c92c457c
--- /dev/null
+++ b/lib/ohai/plugins/rbenv.rb
@@ -0,0 +1,59 @@
+#
+# Author:: Tim Smith (<tsmith@chef.io>)
+# Copyright:: Copyright (c) 2017 Chef Software, Inc.
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+Ohai.plugin(:Rbenv) do
+  depends "languages/ruby"
+  provides "languages/ruby/rbenv"
+
+  collect_data do
+    begin
+      so = shell_out("rbenv versions")
+      # Sample output:
+      #   system
+      # * 2.4.1 (set by /Users/tsmith/.rbenv/version)
+
+      if so.exitstatus == 0
+        rbenv = Mash.new
+        versions = []
+
+        # iterate over each line and build an array of versions
+        # exclude system this provides basically no value to the user
+        # also find the version that starts with * and set it as the default
+        so.stdout.each_line do |line|
+          match = /^(\*)?\s*(\S*)/.match(line)
+          next if match[2] == "system"
+          versions << match[2]
+          rbenv[:default] = match[2] unless match[1].empty? # if it starts with * its the default
+        end
+        rbenv[:versions] = versions
+
+        ver_so = shell_out("rbenv --version")
+        # Sample output:
+        # rbenv 1.1.0
+        if ver_so.exitstatus == 0
+          # sample regex http://rubular.com/r/IzjNV7Yyr3
+          rbenv[:rbenv_version] = /rbenv\s(.*)/.match(ver_so.stdout)[1]
+        end
+
+        languages[:ruby][:rbenv] = rbenv
+      end
+    rescue Ohai::Exceptions::Exec
+      Ohai::Log.debug("Plugin Rbenv: Could not shell_out to rbenv. Skipping plugin")
+    end
+  end
+end
diff --git a/spec/unit/plugins/rbenv_spec.rb b/spec/unit/plugins/rbenv_spec.rb
new file mode 100644
index 00000000..60e75dcc
--- /dev/null
+++ b/spec/unit/plugins/rbenv_spec.rb
@@ -0,0 +1,55 @@
+#
+# Author:: Tim Smith (<tsmith@chef.io>)
+# Copyright:: Copyright (c) 2017 Chef Software, Inc.
+# License:: Apache License, Version 2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+require_relative "../../spec_helper.rb"
+
+describe Ohai::System, "plugin rbenv" do
+  let(:stdout) { <<-OUT
+system
+* 2.4.1 (set by /Users/tsmith/.rbenv/version)
+OUT
+}
+  let(:plugin) do
+    plugin = get_plugin("rbenv")
+    plugin[:languages] = Mash.new
+    plugin[:languages][:ruby] = Mash.new
+    expect(plugin).to receive(:shell_out).with("rbenv versions").and_return(mock_shell_out(0, stdout, ""))
+    expect(plugin).to receive(:shell_out).with("rbenv --version").and_return(mock_shell_out(0, "rbenv 1.1.1", ""))
+    plugin
+  end
+
+  it "sets the rbenv version" do
+    plugin.run
+    expect(plugin[:languages][:ruby][:rbenv][:rbenv_version]).to eql("1.1.1")
+  end
+
+  it "sets the default ruby version" do
+    plugin.run
+    expect(plugin[:languages][:ruby][:rbenv][:default]).to eql("2.4.1")
+  end
+
+  it "versions includes ruby 2.4.1" do
+    plugin.run
+    expect(plugin[:languages][:ruby][:rbenv][:versions]).to include("2.4.1")
+  end
+
+  it "versions doesn't include the system ruby" do
+    plugin.run
+    expect(plugin[:languages][:ruby][:rbenv][:versions]).not_to include("system")
+  end
+end