Add HA recipe

If HA is enabled, this recipe sets up a load balancer for glance
services (registry + api).

The recipe basically just asks for the ip/ports of other servers that
should be behind HA and can be failed over to and sets up load balancers
on the current node.
Check presence of more than one instead one server

As we will want to have servers to which we want to fail over, the
proposal validation should check for at least one instead of exactly one
glance server.
Setup HA and VIP networks in crowbar framework

Check if HA should be enabled. Currently, that means that there are
clusters defined for a given role, i.e. that list of role elements
expands to a differing list of nodes.

Based on that, mark the role as using HA. Then set up virtual IP network
for each cluster.