install-chef-suse: Create empty repos if they don't exist

For all the repositories listed in REPOS_SKIP_CHECKS create an empty skeleton
repository to avoid YaST complaining about missing repositories.

When CROWBAR_FROM_GIT is set also create a skeleton for the Cloud-PTF
repository. In the non CROWBAR_FROM_GIT this is handled by the crowbar RPM.
Merge pull request #1812 from rhafer/master

install-chef-suse: Create empty repos if they don't exist