LU-15938 llog: more checks in llog_reader

LU-15938 llog: more checks in llog_reader

Add more correctness checks and reports in llog_reader:
- better report wrong record length and chunk skipping case
- add tail check: tail id and len should be the same as in head
- better report for gap in record indeces
- test case with two corruption types:
  1) llog has bits set in bitmap beyond file end
  2) corruption in the middle

Lustre-change: https://review.whamcloud.com/48112
Lustre-commit: 386ffcdbb4c9b89f798de4c83a51a3f020542c8b

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: I0c2af6ae2592c94e14e90ead12e28104409313b2
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49214
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>