EX-9280 lipe: lpurge: Add periodical stats on scanned files

EX-9280 lipe: lpurge: Add periodical stats on scanned files

- Report INFO message on each lpurge period.
- Include in the message number of purged files, number of files
for which mirror deleting failed, number of files
which are not purged due to a stale component.
- Reset the periodic counter every period.

Test-Parameters: trivial testlist=hot-pools
Signed-off-by: Alexandre Ioffe <aioffe@ddn.com>
Change-Id: Ib70604c990801b79b0a0356991d45e83ec62db6c
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/54337
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Vitaliy Kuznetsov <vkuznetsov@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>