LU-10218 mdc: propagate changelog errors to readers

LU-10218 mdc: propagate changelog errors to readers

Store errors encountered by the changelog llog reader thread in the
crs_err field of struct changelog_reader_state so that they can be
propageted to changelog readers. In chlg_read() improve the error and
EOF reporting. Return -ERESTARTSYS when the blocked reader is
interrupted. Replace uses of l_wait_event() with
wait_event_interruptible().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I279ec8ca11bfeb67f844acf12e3f7cba8f8aa1e6
Reviewed-on: https://review.whamcloud.com/30040
Tested-by: Jenkins
Reviewed-by: Quentin Bouget <quentin.bouget@cea.fr>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>