Install dev dependencies programmatically

Without shelling out. It should be faster, and it avoids a ruby 2.3
issue where gems installed through a subprocess are not picked up by the
currently running rubygems.

I'm also removing some unneeded `travis_retry` from the TravisCI
configure. These steps shouldn't timeout and if they do, we should
figure out why. Also, they could be hiding other issues not related to
the network. In this case, `travis_retry bin/rake spec:parallel_deps`
was hiding the issue installing dev dependencies being fixed by this
commit.

1 files changed, 8 insertions, 4 deletions

diff --git a/spec/support/rubygems_ext.rb b/spec/support/rubygems_ext.rb
index 5299a7b447..3c8d97b83c 100644
--- a/spec/support/rubygems_ext.rb
+++ b/spec/support/rubygems_ext.rb
@@ -105,10 +105,14 @@ module Spec
     end
 
     def install_gems(gems)
-      deps = gems.map {|name, req| "'#{name}:#{req}'" }.join(" ")
-      gem = ENV["GEM_COMMAND"] || "#{Gem.ruby} -S gem --backtrace"
-      cmd = "#{gem} install #{deps} --no-document --conservative"
-      system(cmd) || raise("Installing gems #{deps} for the tests to use failed!")
+      require "rubygems/dependency_installer"
+
+      gems.each do |name, req|
+        dependency = Gem::Dependency.new(name, req)
+        next unless dependency.matching_specs.empty?
+
+        Gem::DependencyInstaller.new(:document => false).install(dependency)
+      end
     end
   end
 end