Add options to configure provider network mappings for
OpenDaylight

OpenDaylight needs to know the physical network mapping
used with vlan tenant isolation. This is similar to how
the bridge_mappings cofig is used to map the physical
network to the bridge,
i.e. bridge_mappings=physnet1:br-eth1,physnet2:br-eth2.

OpenDaylight needs the physical network device itself:
provider_mappings=physnet1:eth1,physnet2:eth2.

OpenDaylight needs the mapping because the device port is
used when pushing flows. The neutron API's provide the
physical provider network value for example as physnet1.

DocImpact:
Use of VLANs with ML2 and the OpenDaylight mechanism driver
requires OpenDaylight Helium or newer to be installed.

Closes-Bug: #1315492
Change-Id: If7af9ce5735b01c35315a54c79355ca87b72c4b4
Merge "Add options to configure provider network mappings for OpenDaylight"