Cause: If the TUR checker thread becomes unresponsive, multipathd was starting a synchronous TUR check, which could also block.
Consequence: Multipathd could hang when a device that uses the TUR checker failed.
Fix: Multipathd no longer starts a synchronous TUR check when the TUR checker thread becomes unresponsive. It simply marks the path as failed.
Result: Multipathd will no longer hang when a device using the TUR checker fails.