core: Use java.util.Objects.equals(Object, Object)

This patch replaces usages of
org.ovirt.engine.core.common.utils.ObjectUtils.equals(Object, Object)
with the standard JDK7 java.util.Objects.equals(Object, Object) wherever
possible (i.e., no GWT compilation is required).

This patch helps standardize the code, makes it slightly more readable
to novice oVirt developers and may even save a pico-second of
performance.

Change-Id: Ifbce02996fbba804aeabc54a13f2109656f4a2c6
Signed-off-by: Allon Mureinik <amureini@redhat.com>