Rework the substitution pattern for cloud upgrade

Just replacing 3 with 4 replaces too much. E.g. SLE11-SP3 -> SLE11-SP4.
Restrict it to just replace the cloud version.
Use --gpg-auto-import-keys --no-gpg-checks for zypper during upgrade testing

To avoid complaints about unsigned Cloud-PTF repo
No need to install crowbar-barclamp-trove during upgrade-test

suse-cloud-upgrade takes care about that already
Merge pull request #125 from rhafer/suse-cloud-upgrade

Fixes for suse-cloud-upgrade