core: Eliminate unneeded updates to VdsDynamic

This patch tries to minimize updates to VdsDynamic by checking the
database value before updating the entity.

Change-Id: Icab3ed7d251573f150d28f966d0ad2363ecc3441
Bug-Url: https://bugzilla.redhat.com/1016634
Signed-off-by: lzelkha@redhat.com <lzelkha@redhat.com>