ssh before shelve to avoid ssh failures

The current test to attach / detach volumes on a shelved
server, performe the shelves before having verified that the
server was ssh-able. This makes failures in the VM setup
before and after shelve non distinguishable.

Adding an ssh check before shelve.

Change-Id: I0ec375d24f6aac69a79578180efe5018b25a1bdd
1 file changed