resource-discovery location constraint option

Location constraints now have the 'resource-discovery' option, which allows probes to be selectively enabled/disabled per resource/node.

resource-discovery=[always|never|exclusive]

Example: never probe for rsc1 on node1, the rest of the nodes will be probed for rsc1
<rsc_location id="location" node="node1" rsc="rsc1" score="-INFINITY" resource-discovery="never" />

Example: only probe for rsc1 on node1 and node2  (rsc1 will not be probed on any other nodes)
<rsc_location id="location1" node="node1" rsc="rsc1" score="0" resource-discovery="exclusive" />
<rsc_location id="location2" node="node2" rsc="rsc1" score="0" resource-discovery="exclusive" />