This adds a new IP manager driver for configuring addresses
and routes via keepalived instead of directly. It used when
the logical resource is configured to be highly-available,
according to configuration pushed by the orchestrator.
We rely on a 'ha_resource' flag attached to the main config
dict to enable it, and use specific HA config about peers and
cluster priority contained in the 'ha_config' section of the
main config.
The resulting keepalived cluster contains a VRRP instance for
each interface, with the exception of the management interface.
Partially-implements: blueprint appliance-ha
Change-Id: I5ababa41d65642b00f6b808197af9b2a59ebc67a
02383adf64