add gems to cache
improved gem installation
Merge branch 'master' into features/gem-cache
reset gem_version before parsing gem_install parameters
check rvm_path/gem-cache before installing gems with gem_install
Merge pull request #2481 from wayneeseguin/features/gem-cache

RVM offline installation: rvm trying to connect to rubygems.org  to get https://rubygems.org/specs.4.8.gz