engine : Remove unneeded VdsDynamic updates

VdsUpdateRuntimeInfo updates VdsDynamic even if it hasn't
changed. This patch fixes it, and reduces the number of DB
updates.

Change-Id: I0254991f424490d848f84fc951e64787bf54d7bc
Bug-Url: https://bugzilla.redhat.com/1016634
Signed-off-by: lzelkha@redhat.com <liran.zelkha@gmail.com>