Initial support for HA by assuming shared storage

We do not handle in any way the shared storage here; it could be
something to look at.
Add ability to use shared storage
Use new synchronization helpers to avoid races when deploying with HA

This helps avoid races when creating the pacemaker resources, either
because rabbitmq is not installed on one node yet (resulting in the
pacemaker resource not being runnable on that node) or because the
pacemaker resources are created at the same time on multiple nodes.
Use new Chef::Provider::CrowbarPacemakerService provider
On HA, wait for the vhostname to be defined in DNS

The rabbitmq daemon needs the vhostname to be resolvable, so we wait
for that before starting the pacemaker resource.
Force a DNS update in apply_role_pre_chef_call for HA

The virtual hostname needs to be resolvable for the cookbook to
successfully run.
add support for DRBD