r=johann,shadow

- fixes ptlrpcd blocking on very long reply unlink waiting. To do so new rpc phase introduced
RQ_PHASE_UNREGISTERING in which request stay until we have reply_in_callback() called by lnet
signaling that reply is unlinked. All requests in this state are skipped in processing by prlrcd
instead of waiting n * 300s on each of them. This allows ptlrpcd to process other rpcs in the set;

- make sure that inflight count is coherent with being present on sending or delay list. That is,
if we see inflight != 0, rpc must be on one of these lists. This is very helpful in
ptlrpc_invalidate_import() to show all rpcs still waiting after invalidating import;

- in ptlrpc_invalidate_import() wait maximal rq_deadline - now from all inflight rpcs instead of
obd_timeout which may be much longer. If calculated timeout is 0, obd_timeout is used. This fixes
the issue that rq_deadline - now > obd_timeout (very easy to see in logs) which led to inflight !=
0 assert because inflight rpcs timed out later than our wait period is finished;

- in ptlrpc_invalidate_import() wait forever for rpcs in UNREGISTERING phase. Check in assert for
inflight == 0 for wait timed out case if no rpcs in UNREGISTERING phase. Only those in
UNREGISTERING phase are allowed to stay longer than obd_timeout;

- added ptlrpc_move_rqphase() function. All phase changes go through it. Add debug_req() there to
track down all phase changes;

- conf_sanity.sh test_45 added to emulate very long reply unlink and also situation when
rq_deadline - now > obd_timeout;

- do not wait forever in ptlrpc_unregister_reply() for async case (using it from sets). sync case
left unchanged;

- make sure that ptlrpc_set_next_timeout() yields 1s timeout (instead of 0s) for the set with rpcs
in "unregistering" stage to prevent ptlrpcd from sleeping forever and hanging in test_45;

- in ptlrpcd() make sure that we do not sleep on 0 timeout.