Do not crash if a ceilometer-agent node is not a compute node
Always start the ceilometer-agent-compute service resource

We should not just enable it, but start it too.
Disable and stop ceilometer-agent-compute if node is not a compute node

We know the agent can't work in this case.
Merge pull request #148 from vuntz/fix-crash

Do not crash if a ceilometer-agent node is not a compute node