A stonith device using fence_scsi fails to start with "ERROR:root:Failed: device '<device>' does not exist" in a RHEL 7 High Availability cluster

Issue

• I can't get my fence_scsi stonith device started
• I'm seeing errors from fence_scsi in pcs status output
• stonith-ng reports "Failed: device does not exist" for my fence_scsi device on startup

scsi_start_0 on ha-2 'unknown error' (1): call=595, status=Error, exitreason='none',    last-rc-change='Fri Apr 29 12:53:50 2016', queued=0ms, exec=1097ms

May  2 12:06:44 node2 fence_scsi: Failed: device "/dev/disk/by-id/wwn-0x068fc6156cc001b16f7045767946ca1c" does not exist
May  2 12:06:44 node2 fence_scsi: Please use '-h' for usage
May  2 12:06:44 node2 ntpd[4186]: Deleting interface #10 eth0, 172.16.0.60#123, interface stats: received=0, sent=0, dropped=0, active_time=527 secs
May  2 12:06:45 node2 fence_scsi: Failed: device "/dev/disk/by-id/wwn-0x068fc6156cc001b16f7045767946ca1c" does not exist
May  2 12:06:45 node2 fence_scsi: Please use '-h' for usage
May  2 12:06:45 node2 stonith-ng[2536]:    error: Operation 'on' [50911] (call 3 from crmd.2540) for host 'node2' with device 'scsi' returned: -201 (Generic Pacemaker error)
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [ WARNING:root:Parse error: Ignoring unknown option 'port=node2' ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [  ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [ ERROR:root:Failed: device "/dev/disk/by-id/wwn-0x068fc6156cc001b16f7045767946ca1c" does not exist ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [  ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [ Failed: device "/dev/disk/by-id/wwn-0x068fc6156cc001b16f7045767946ca1c" does not exist ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [  ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [ ERROR:root:Please use '-h' for usage ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [  ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [ Please use '-h' for usage ]
May  2 12:06:45 node2 stonith-ng[2536]:  warning: scsi:50911 [  ]
May  2 12:06:45 node2 stonith-ng[2536]:   notice: Couldn't find anyone to fence (on) node2 with any device
May  2 12:06:45 node2 stonith-ng[2536]:    error: Operation on of node2 by <no-one> for crmd.2540@node2.88b94800: No route to host