core: Fix confusing getStorageDomainDao() method

Removed getStorageDomainDao() and used the pre-existing
getStorageDoaminDAO() instead.

Change-Id: I7f4b339849f8e8aa13c9d4ad26b34a1fb63cdf32
Signed-off-by: Allon Mureinik <amureini@redhat.com>