Rename onadmin_prepare_sles_repos to onadmin_prepare_sles11sp3_repos
Rename onadmin_prepare_sles_repos to onadmin_prepare_sles11sp3_repos

This function is only called for setting up sles11sp3 repos, so it
makes sense to rename it to that and cleanup the code.

vmoravec/automation,SUSE-Cloud/automation,aspiers/automation,vmoravec/automation,SUSE-Cloud/automation,SUSE-Cloud/automation,vmoravec/automation,SUSE-Cloud/automation,aspiers/automation,gosipyan/automation,gosipyan/automation,gosipyan/automation,vmoravec/automation,aspiers/automation,aspiers/automation,gosipyan/automation