LU-8320 llog: prevent llog ID re-use.

LU-8320 llog: prevent llog ID re-use.

The new llog ID generated in simple manner by
increment of the last used OID within the same FID
sequence. Therefore OID can cycle through zero and
match some very old llog file which is still in use
or orphaned. Patch skips such llog IDs. Also patch
replaces several assertions with sanity checks in
llog_write() path.

Signed-off-by: Mikhal Pershin <mike.pershin@intel.com>
Change-Id: Iffd7e61f75fdb554ae03c8a4b685cd2aff648c24
Reviewed-on: http://review.whamcloud.com/21144
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>