LU-10467 ptlrpc: convert waiting in ptlrpc_hr_main()

LU-10467 ptlrpc: convert waiting in ptlrpc_hr_main()

This is a basic conditional wait. Instead of using
l_wait_condition() use the linux standard wait_event_idle().

Change-Id: I5c81914de003468ac20b6c65f1b6bee2d4cf6891
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/37696
Reviewed-by: Neil Brown <neilb@suse.de>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>