hacluster helper causes deployment failures if relations are made before config options are set

The hacluster helper (and subsequently charms such as keystone), are not tolerant of missing cluster data. This causes them to fail a hook if the ha-relation-joined hook is hit before the charm config option is applied.

Instead of failing the deployment, the helper and affected charms should probably go into a blocked state, awaiting ample configuration information.

http://paste.ubuntu.com/14075570/

# Unit log & trace
# NOTE: In this output, I patched get_hacluster_config() in charmhelpers/contrib/hahelpers/cluster.py to spit out the missing data list along with the error.

unit-keystone-2[9632]: 2015-12-17 17:01:45 ERROR unit.keystone/2.juju-log server.go:268 ha:3: Insufficient config data to configure hacluster: ['vip']
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 Traceback (most recent call last):
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 File "/var/lib/juju/agents/unit-keystone-2/charm/hooks/ha-relation-joined", line 647, in <module>
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 main()
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 File "/var/lib/juju/agents/unit-keystone-2/charm/hooks/ha-relation-joined", line 639, in main
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 hooks.execute(sys.argv)
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 File "/var/lib/juju/agents/unit-keystone-2/charm/hooks/charmhelpers/core/hookenv.py", line 704, in execute
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 self._hooks[hook_name]()
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 File "/var/lib/juju/agents/unit-keystone-2/charm/hooks/ha-relation-joined", line 498, in ha_joined
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 cluster_config = get_hacluster_config()
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 File "/var/lib/juju/agents/unit-keystone-2/charm/hooks/charmhelpers/contrib/hahelpers/cluster.py", line 295, in get_hacluster_config
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 raise HAIncompleteConfig
unit-keystone-2[9632]: 2015-12-17 17:01:45 INFO unit.keystone/2.ha-relation-joined logger.go:40 charmhelpers.contrib.hahelpers.cluster.HAIncompleteConfig
unit-keystone-2[9632]: 2015-12-17 17:01:45 ERROR juju.worker.uniter.operation runhook.go:107 hook "ha-relation-joined" failed: exit status 1

# Juju stat (before charm config options were applied)

[Services]
NAME STATUS EXPOSED CHARM
hacluster false local:trusty/hacluster-0
keystone error false local:trusty/keystone-0
mysql unknown false local:trusty/mysql-326

[Units]
ID WORKLOAD-STATE AGENT-STATE VERSION MACHINE PORTS PUBLIC-ADDRESS MESSAGE
keystone/0 error idle 1.25.1 1 10.5.24.161 hook failed: "ha-relation-joined" for hacluster:ha
  hacluster/0 active idle 1.25.1 10.5.24.161 Unit is ready and clustered
keystone/1 error idle 1.25.1 2 10.5.24.162 hook failed: "ha-relation-joined" for hacluster:ha
  hacluster/1 active idle 1.25.1 10.5.24.162 Unit is ready and clustered
keystone/2 error idle 1.25.1 3 10.5.24.163 hook failed: "ha-relation-joined" for hacluster:ha
  hacluster/2 active idle 1.25.1 10.5.24.163 Unit is ready and clustered
mysql/0 unknown idle 1.25.1 4 10.5.24.164

[Machines]
ID STATE VERSION DNS INS-ID SERIES HARDWARE
0 started 1.25.1 10.5.24.160 3bbb58db-0cf5-4bc2-95c2-7df3e490f587 trusty arch=amd64 cpu-cores=1 mem=1536M root-disk=10240M availability-zone=nova
1 started 1.25.1 10.5.24.161 ac00dcdc-0abf-4b25-945c-12b0f42e7e7c trusty arch=amd64 cpu-cores=1 mem=1536M root-disk=10240M availability-zone=nova
2 started 1.25.1 10.5.24.162 87f381a2-efeb-4b71-916a-c53cbf31853f trusty arch=amd64 cpu-cores=1 mem=1536M root-disk=10240M availability-zone=nova
3 started 1.25.1 10.5.24.163 136322e1-296b-419a-9419-b2f625e7ba90 trusty arch=amd64 cpu-cores=1 mem=1536M root-disk=10240M availability-zone=nova
4 started 1.25.1 10.5.24.164 d3cf34b4-5d89-42d4-8a5a-b16de1b21941 trusty arch=amd64 cpu-cores=1 mem=1536M root-disk=10240M availability-zone=nova