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 and make sure the DNS is configured, as the setup
recipe in the glance cookbook needs to resolve virtual IPs in the cluster.
Move method for fetching HAproxy servers to lib

This can be reused across barclamps, so move it into GlanceHelper module
for now. Refactor even further up later.
Centralize network settings

To make configuring / fiddling with network settings easier, centralize
them into a helper method, returning a hash w/ API + registry network
configuration.
Add caching to HA server lookups