LU-1299 clio: a combo patch to fix cl_lock

LU-1299 clio: a combo patch to fix cl_lock

In this patch, the following issues are fixed:
* redefine cl_lock_error(). There are two kinds of error when
  enqueuing a cl_lock: internal errors return from server side and
  local error for example interrupted by signal when waiting for a
  lock. Obviously the latter one is not fatal so we shouldn't err the
  lock out;
* for fault handling, only signal SIGKILL and SIGTERM is not allowed;
* handle return code of ll_fault correctly;
* redefine ->unuse() to release resource it held if enqueuing lock
  failed;
* in cl_lock_hold_release(), only CLS_CACHED mode lock will be cached,
  for locks in other states, they will be cancelled voluntarily;
* fix the problem that cfs_block_sigs() is wrongly used as
  cfs_restore_sigs() and implementation of cfs_block_sigs() was wrong
* other minor fixes.

Signed-off-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Change-Id: Ice6d237d367c54bfd84a4a33cea8a4c1081e7696
Reviewed-on: http://review.whamcloud.com/2654
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Hudson
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>