Loading specific version of rhoelements gems based on app sdkversion

@genywind : This pull request is first made into 4.0.0 stable branch. How to test it:
install various versions of rhoelements gems (4.0.x, 4.1.x), rhoconnect-client gems. 
Use any rhodes app with app_type: rhoelements (or specify extension rhoconnect-client). Change sdkversion in build.yml to 4.0.0 . Specify path to this branch in sdk param. Build an app - latest 4.0.x gem should be picked up and not the 4.1.x.
Once the functionality is verified - I will create additional pull requests  into 4.1. stable & master.