Bug 8476 Add support for logical switch replication mode

Bug 8476 Add support for logical switch replication mode

With OVS 2.6, the Logical Switch table, in the hardware_vtep schema, has
a new field, replication_mode. This bug will be used to add support to
netvirt, ovsdb, and genius for setting the replication_mode of logical
switches. The default will be for ODL to set the replication_mode
to "source_node" when creating logical switches.

Refer to [1] for more details on replication_mode.

[1] http://openvswitch.org/support/dist-docs/vtep.5.html

Try/catch block in place to handle case where schema
version does not support replication_mode.

Tested this with OVS 2.5, which does not support replication_mode.
Verified that logical switch is created.

Debug log will be generated when schema version does
not support replication_mode (same check as PhysicalSwitchUpdate).

Change-Id: I374ba52ff5517dacb6af498f34b7e58638f46463
Signed-off-by: Victor Pickard <vpickard@redhat.com>