display OCF exit reason string.


This is the pacemaker implementation part of this resource-agent patch.
https://github.com/ClusterLabs/resource-agents/pull/465

This gives OCF scripts the ability to pass back a failure reason string before exiting that Pacemaker can then display in its crm_mon output.   Now we can have some context in the actual status as to why a resource agent failed with "OCF_ERR_GENERIC" rather than having to parse though log files.
Shoudn't this code test for the attribute "exit-reason", not "exitreason" ?