Update db password migration script to remove node attributes

On update, we want to use the db password from the proposal / role, and
not the one that might have been generated on the node (through the
cookbook). As the password is a "normal" attribute on the node, but a
"default" attribute on the role, the old one from the node is used.
Which means we really need to remove it to get the new one used.

To minimize config changes, we actually import the password from one
node (which should be good enough in most cases as we allow only one
neutron proposal, so only one node should have the password).
Merge pull request #65 from vuntz/drop-db-node

Update db password migration script to remove node attributes
Rename [:ha][:enabled] attribute to [:ha][:server][:enabled]

This will allow us to introduce :ha][:l3][:enabled] later to differentiate
between the HA setups of neutron-server and l3-agent.
Skeleton code for l3-agent ha

This introduces the HA enablement pieces for the l3-agent. Currently this l3_ha
recipe is still a dummy and does nothing useful.
Implement l3_ha recipe

Create pacemaker primitive, group and clone for the various neutron agents.
Setup the neutron-ha-tool to perform automatic migrations of offline
routers.
l3_ha: Don't start l3-agent when using "vmware" networking
Include linux-bridge/ovs-agent into the l3 HA group
Add an order constraint for neutron-ha-tool

This should make sure that the neutron-agents clone is started before the
neutron-ha-tool primitive. Otherwise neutron-ha-tool might cause unneeded
router migrations.
Setup a clone resource for neutron-server
Use pacemaker service provider when HA is enabled
Derive the resource agent name attributes from the service names
Fix actions on the pacemaker resources for neutron-server
Only install ha-tool package on platforms that have it
Use synchronization helpers in l3_ha to avoid races when deploying with HA