Remove cluster member

Remove node from a cluster. See https://trello.com/c/xarZEs6g/846-ha-support-removing-nodes-from-clusters

Originally https://github.com/crowbar/barclamp-pacemaker/pull/100, but rebased and requested against master 

https://github.com/crowbar/barclamp-crowbar/pull/1011 is needed so the remove role get correctly deleted after it is used once.
Is there a way you could execute the whole recipe only under a certain condition?
something like 
```ruby
unless "some flag that says node is still a cluster member and is not intended to be removed"
```
Then you would not be so dependent on https://github.com/crowbar/barclamp-crowbar/pull/1011
And even if the crowbar patch is merged but for whatever reason the `pacemaker-cluster-member_remove` role would still be in the runlist, this would at least be a double check.

for example my deactivation recipe of e.g. `heat` which is defined in the `heat-server_remove` role only runs 
```ruby
unless node[:roles].include?('heat-server')
```
crowbar removes `heat-server` from `node[:roles]` when i hit `deactivate`, so i can rely on that flag.
so if in your case the `pacemaker-cluster-member_remove` role is still in the runlist, the `remove_from_cluster.rb` recipe would not be executed.
maybe in your scenario there is a similar flag?