Close the SouthboundHandler Executor Gracefully

During the OSGi "stop" method try and close the Executor gracefully.
Stop accepting new work by calling shutdown()
Wait a given time for  the current task to terminate before issuing a
shutdownNow()

Fixes bug 281

Change-Id: I0823a3dce87e67ca3e5d18640e9ecd5d4e75b7ba
Signed-off-by: Dave Tucker <djt@redhat.com>
Merge "Close the SouthboundHandler Executor Gracefully"