Added cluster aware mdsal utils class to net-virt.

Added cluster aware mdsal utils class to net-virt.

Looks like while code cleanup we removed the MdsalUtils.java from the master branch
and while merging master branch to net-virt-clustering, it got removed as well.
Net-virt-clustering had a modified version of MdsalUtils.java, where put/merge/delete
transactions are only done by the master instances of net-virt. ClusterAwareMdsalUtils
class bring those changes back.

Change-Id: I1d5353572c408e519d7a3cc75356b73436dae147
Signed-off-by: Anil Vishnoi <vishnoianil@gmail.com>