core: Add isEmpty Check to MacPoolManager

This patch adds an isEmpty() check to the
freeMacs method, in the MacPoolManager,
to avoid entering a synchronized block when
unnecessary.

Change-Id: Id34bae38c0a05e1e148267950ca1ca464b36daea
Bug-Url: https://bugzilla.redhat.com/903572
Signed-off-by: Muli Salem <msalem@redhat.com>
core: Remove Mac Addresses When DC Removed

This patch removes the Mac Addresses of the vNics
that are under the Data Center that is being removed.

Change-Id: I5b6d473b4921de12fbd68bdaf2fc058662ed3a06
Bug-Url: https://bugzilla.redhat.com/903572
Signed-off-by: Muli Salem <msalem@redhat.com>