EX-8441 lipe: lamigo fix compatibility with older lustre

EX-8441 lipe: lamigo fix compatibility with older lustre

- lfs mirror extend may dump help text either to stdout or stderr.
  Lamigo will adopt both cases
- Make correct exit from loop when ssh remote session fails
- Skip hot-pools tests 75a,75b,75c if lfs mirror extend
  does not support --stats-interval
- Minor code fixes

Test-Parameters: trivial testlist=hot-pools
Signed-off-by: Alexandre Ioffe <aioffe@ddn.com>
Change-Id: Iba035043bc4868e7898f3739d03607d5d3e21574
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/52898
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>