l3 support (partial): move event dispatch from southBoundHandler

l3 support (partial): move event dispatch from southBoundHandler

The event handling in southbound needs to move to a common location, so
neutron callbacks can also be enqueued. With these changes, we can now
create a nothBoundHandler, which will take neutron events and enqueue
envents to a shared dispatcher.

Patch set 3: Added copyright headers for the newly added files.
Patch set 4: Make neutron port handler use event dispatcher.
Patch set 5: Fix link to test log
Patch set 6: Use OSGI whiteboard pattern to register event handlers with the dispatcher.
Patch set 7: Code review changes.

Script for creating coke tenants in devstack:
https://gist.github.com/1ba897e7cde8dbd87fe8

Starting odl command:
./run.sh -virt ovsdb -Xms40m -Xmx1024m -XX:MaxPermSize=1024m

LogLevel:
setLogLevel org.opendaylight.ovsdb.openstack.netvirt.providers.OF13Provider trace
setLogLevel org.opendaylight.ovsdb.openstack.netvirt.api.EventDispatcher trace
setLogLevel org.opendaylight.ovsdb.openstack.netvirt.SouthboundHandler debug
setLogLevel org.opendaylight.ovsdb.openstack.netvirt.PortHandler debug

Log of test:
createTenants: https://gist.github.com/44b4ec87f3c89fe5683e
osgi: https://gist.github.com/47627762ed9d9b474b29

Change-Id: Ieaf8a91e65f82c37ac5fddd2ec824311cd1d5771
Signed-off-by: Flavio Fernandes <ffernand@redhat.com>