LU-11392 tests: check race for llog_process_thread

LU-11392 tests: check race for llog_process_thread

The patch adds 10h test at llog_test which runs at 60a sanity.
It reproduces a race between llog_process_thread and llog_add.
The llog should be wrapped so it has old data on disk and zero at
bitmap.
1. llog_process_thread reads part of llog at buffer.
1. process a last record, checks the next record fields
2. llog_add adds a record and marks new record at bitmap
1. check bitmap flag and process the old record from buffer

Test-Parameters: testlist=sanity envdefinitions=ONLY=60a
Cray-bug-id: LUS-6287
Signed-off-by: Alexander Boyko <c17825@cray.com>
Change-Id: Ic89c81dd918d856f441df4d3257377e09b91a8cc
Reviewed-on: https://review.whamcloud.com/33192
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alexander Zarochentsev <c17826@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>