gem_package poor interaction with omnibus via memoized Gem environment variables

when running under omnibus with a system ruby and an omnibus ruby, the gem environment is mishandled by chef and a gem_package will bleed memoized state pointing at the system ruby into later resources.

this code will fail (assuming that ruby-shadow is /not/ installed in the system ruby):

chef_gem "ruby-shadow"

gem_package "fpm"

user "foobar" do
  comment "FOO BAR"
  uid 6666
  gid "sysadmin"
  home "/home/foobar"
  shell "/bin/zsh"
  password "$1$5PVdQna7$XDmd2Eeywh5gIIcCk3Prc."
end

in order to make the user resource not throw a MissingLibrary exception, you can comment out the gem_package "fpm" line and all will be well...

the chef_gem "ruby-shadow" line is not really part of the bug, that is just there to assert that the library is really present in the omnibus ruby...