Cache dependencies for CI
Cache dependencies for CI

Caching dependencies for CI to help speed up installing gems
significantly and avoid too many requests to RubyGems.org.

Signed-off-by: J.R. Garcia <837382919d8fe61d4198de0c3cb7269cb0eb414f@vmware.com>

10xEngineer/rbvmomi,vmware/rbvmomi,10xEngineer/rbvmomi