webadmin: clean connection on new GlusterFS failure

StorageListModel -> saveNewGlusterStorage() -> AddStorageServerConnection:
Set connection ID (using action's return value) to enable connection
clean-up on failure [as 'StorageListModel -> cleanConnection()' invokes
RemoveStorageServerConnection iff connection's ID exists].

Change-Id: Id50f5230e5548e50ff17a7bc6af1bf098ccb8c15
Bug-Url: https://bugzilla.redhat.com/1021882
Signed-off-by: Daniel Erez <derez@redhat.com>