Fixes #6927 - make the subscription identity check language independent

Check exit status of `subscription-manager identity` should be enough to find
out if the system was registered or not.
Fixes #8229: Fixing RVM gpg key install error on devel installs.
Merge pull request #134 from ehelms/fixes-8229

Fixes #8229: Fixing RVM gpg key install error on devel installs.
Merge pull request #132 from iNecas/issue/6927

Fixes #6927 - make the subscription identity check language independent