Engine: include only needed sub-engine files

Prevents the error Gem::Package::TooLongFileName on bundle install
due to file paths being above the limit
Engine: Adding Rubocop code style checker for better Jenkins output.
Merge pull request #3435 from jlsherrill/engine_update

Engine: include only needed sub-engine files
Merge pull request #3449 from ehelms/engine-checkstyle

Engine: Adding Rubocop code style checker for better Jenkins output.
Engine: Fixing lint problems detected by rubocop
Merge pull request #3456 from daviddavis/temp/20131204071804

Engine: Fixing lint problems
Merge pull request #3453 from Katello/engine

PR: Request merge of engine branch to master
Merge branch 'master' into subscriptions-widget