QA: Extend cluster QA wrt enabled storage types

This extends the QA scripts to test the changes in 'gnt-cluster init',
'gnt-cluster info', and 'gnt-cluster modify' with respect to enabled
storage types.

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>