Add config variables for OVSDB and controller

Add the ability to set the local-ip (ODL_LOCAL_IP) as well as the OVSDB
manager IP (ODL_MGR_IP) via configuration variables. These default to
the following if unconfigured:

ODL_LOCAL_IP ---> HOST_IP
ODL_MGR_IP   ---> What you set in "url" for the ML2 ODL configuration.

Change-Id: I77ead1206da5e0de0214189a6e43bd08d00c6b6d