[sle12sp5][desktop] test fails in boot_to_snapshot
Testcase "boot_to_snapshot" in SLED12SP5 can no longer pass after changes made in https://github.com/os-autoinst/os-autoinst-distri-opensuse/issues/7773 .
After some discussion with yifanjiang, we decided that this testcase is different between SLES and SLED, so we revert to older behavior.
So I added a new testcase "boot_to_snapshot_sled", it passed at: https://openqa.suse.de/tests/3203245
And I will use it to replace "boot_to_snapshot".