Drop rubygems install for trusty / icehouse

ruby packaging in trusty includes ruby gem command already. Also
installing rubygems is unnecessary and results in multiple ruby
toolchains being installed.

Change-Id: Ic5bc93c0926c29fa5116f9cf7a0a3b23addda3ba
Closes-Bug: #1295327
Disable supplemental_repo for trusty+icehouse

The supplemental_repo is not expected to be needed for icehouse on
trusty.

Change-Id: I58bd59b9622b2d7124f6f42388f38c2128170463
Implements: blueprint separate-puppet-repo
Merge "Drop rubygems install for trusty / icehouse"
Merge "Disable supplemental_repo for trusty+icehouse"
Merge remote-tracking branch 'origin/master' into icehouse