Rough musings towards an MD-SAL OVSDB SB

Rough musings towards an MD-SAL OVSDB SB

This patch is incomplete, it only manages to accept
ovsdb connections and log them, but its a start.

PatchSet2: Added a simple starting model around tunneling
PatchSet3: Added additional tunnel info
PatchSet4: Added ovsdb.yang model.  Separated tunnel into tunnel.yang
PatchSet5: Renamed tunnel.yang to overlay.yang.  Added topology-type info.
PatchSet6: Added in dummy DataChangeListener for OvsdbNodes.
           Moved mapping functions into a mapping class.
           Handled tracking of OvsdbClients
PatchSet7:  Responded to comments:
            Fixed whitespace
            Fixed parent for aggregator
            Fixed features from odl-southbound- to odl-ovsdb-southbound-
PatchSet10: Added DataChangeListner to listen for new ovsdb-nodes in topology
            and connect to them.
PatchSet15: Response to Colin's comments
PatchSet18: Fixed feature dependencies.  Depends on patch
            https://git.opendaylight.org/gerrit/#/c/14791/ in controller
PatchSet19: Fixed small error in startup order

Change-Id: I13179ec4a1c338ae239f79c0812adf4bc4d6e76d
Signed-off-by: Ed Warnicke <eaw@cisco.com>