Set profiler only for postgresql not mysql

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10156#note_26812609

config/initializers/rspec_profiling.rb

@@ -38,7 +38,7 @@ if Rails.env.test?
     end
   end
 
-  if ENV.has_key?('CI')
+  if ENV.has_key?('CI') && ENV['GITLAB_DATABASE'] == 'postgresql'
     RspecProfiling::VCS::Git.prepend(RspecProfilingExt::Git)
     RspecProfiling::Run.prepend(RspecProfilingExt::Run)
   end