Implement helpers to keep node ressources in sync

Worked on the lwrp sync_mark to enable chef to keep nodes in sync.
The lwrp sync_mark action :create will set a sync mark in the node attributes
(an identifier  and a mark) and save that mark on the server.

With the lwrp sync_marc action :wait a node will halt recipe execution until
a sync mark (identifier and a mark) will be set to mark-finished on all nodes
in the cluster. This works also if that particular mark has never been set on the node
where the action is run.

Also used the lwrp once in the default recipe
Issues:
  - Timeout is probably not working properly yet?
  - Does node_count always give the right numer of nodes?
  - resource.revision is not used atm, in general a cleanup is needed
Implement helpers to keep node ressources in sync

Included feedback from first review.
Seems to work in general.

Issues:
- Nodes that are currently offline are also counted. Those
  nodes won't ever transition to finished, and the waiting method
  always fail. Does not happen when all nodes are online

- I think I got the revision usage wrong, the way it is handled now
  is not much different from my original way
syncing nodes for HA usage

- Fixed log messages
- Usage of revison should be fine now
Solved offline nodes issue

CrowbarPacemakerHelper::cluster_nodes got extended is now able to only
return nodes that are currently online by crowbar timeouts. This should
solve the problem we run into, when a node in the cluster is offline. A offline
node will never transition to finished and cause the wait_for_mark method to
timeout.

The error window is reduced to the time frame when nodes go offline within 20
minutes before the chef-client run.
Work in feedback on old pr

- Expanded lwrp, added a new sync actions
- Renamed cluster-related helper method
- Removed set_mark method
- Dropped '-finished' code
- Dropped offline distinction for node count
- Restored old founder-related methods
- Updated comments, log information
Reworked commit

- added cluster name to the identifier string
- investigated why revision attribute tag is required for the lwrp
- added again accidentally deleted code
- comments cleanup
Merge pull request #7 from nkrinner/sync-marks

Sync marks