LU-14207 mgs: delete "add failnid" sections on replace_nids

LU-14207 mgs: delete "add failnid" sections on replace_nids

Replace_nids left old nids in add_conn field of failnid
section of client llog. This leads to connecton errors.

Let's delete such sections. New failnids, if any, are
added by replace_nids.

Change-Id: I7fab00827035bd864aeb95fb4852a59c458bb2ba
HPE-bug-id: LUS-9440
Signed-off-by: Artem Blagodarenko <artem.blagodarenko@hpe.com>
Reviewed-by: Vladimir Saveliev <c17830@cray.com>
Reviewed-by: Alexander Boyko <c17825@cray.com>
Tested-by: Jenkins Build User <nssreleng@cray.com>
Reviewed-on: https://review.whamcloud.com/40930
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>