High: shellfuncs: set exit error reason string

Error strings reported using 'ocf_error_reason' will
be formatted in a special way that allows cluster resource management
daemons like Pacemaker record a string describing why a resource
failure occurred.
Low: Dummy: add sample usage of 'ocf_exit_reason'
Merge pull request #465 from davidvossel/exit-msg

Ability to pass exit reason string on stderr to cluster manager