LU-14093 mgc: rework mgc_apply_recover_logs() for gcc10

LU-14093 mgc: rework mgc_apply_recover_logs() for gcc10

rework mgc_apply_recover_logs() to use a separate buffer of
appropriate size so that gcc10 doesn't complain:
mgc_request.c:1506:24: error: argument 4 may overlap destination
        object [-Werror=restrict]
 1506 |        pos += sprintf(obdname + pos, "-%s-%s", cname, inst);

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Ice863b412475e53705dc6523ab30ba613244bd90
Reviewed-on: https://review.whamcloud.com/40484
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>