Prevent blank Storage Manger names.

It currently allows to pass a nil name of the storage manager, effectively making the 'show' view not-working because of trying to use `+' method on nil. This commit rectifies this issue by enabling name presence check in the model.

https://bugzilla.redhat.com/show_bug.cgi?id=1129718
Merge pull request #383 from mfalesni/sm_validate_name

Prevent blank SM names