core: No Search for isVmTemlateWithSameNameExist

Replaced VmTemplateCommand.isVmTemlateWithSameNameExist(String)'s
implementation with a simple DAO call instead of invoking an expensive
Search query.

Change-Id: I5e9d57ad4d46b22d98529e07a2c67fed968d45cf
Signed-off-by: Allon Mureinik <amureini@redhat.com>