LU-10467 lustre: use wait_event_idle() where appropriate.

LU-10467 lustre: use wait_event_idle() where appropriate.

When l_wait_event() is passed an 'lwi' which is initialised
to all zeroes, it behaves exactly like wait_event_idle():
 - no timeout
 - not interrupted by any signal
 - doesn't add to load average.

So change all these instances to wait_event_idle(), or in two cases,
to wait_event_idle_exclusive().

There are three ways that lwi gets set to all zeros:
	struct l_wait_info lwi = { 0 };
	lwi = LWI_INTR(NULL, NULL);
	memset(&lwi, 0, sizeof(lwi));

Change-Id: Ia6723cbe248ce067331a002e5e9d54796739c08a
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Reviewed-on: https://review.whamcloud.com/35971
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Petros Koutoupis <pkoutoupis@cray.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>