Try to make Runner.rb transactional safe

lib/runner.rb

@@ -15,10 +15,12 @@ class Runner
     return true if @build.canceled?
-    if @project.no_running_builds?
-      run
-    else
-      run_later
+    run_in_transaction ? run : run_later
+  end
+
+  def run_in_transaction
+    ActiveRecord::Base.transaction do
+      build.run! if project.no_running_builds?
     end
   end
@@ -37,8 +39,6 @@ class Runner
     commands = commands.lines.to_a
     commands.unshift(prepare_project_cmd(path, build.sha))
-    build.run!
-
     Dir.chdir(path) do
       commands.each do |line|
         status = command(line, path)
@@ -91,7 +91,7 @@ class Runner
     @process.environment['CI_SERVER_REVISION'] = GitlabCi::Revision
     @process.environment['CI_BUILD_REF'] = build.ref
-    
+
     @process.start
     build.set_file @tmp_file.path