EX-3342 tests: fix Lustre ver in skip checks in sanity-flr

EX-3342 tests: fix Lustre ver in skip checks in sanity-flr

Many patches land to the EXAScaler branches as ports from
other branches.  Sometimes the tests that are included with
the ported patches check the version of Lustre to ensure
that the feature it tests exists in this version of Lustre.
These version values are not always changed when patches
are ported from one branch to another.

Change Lustre test suite version checks to be relative to
this branch. Sanity-flr test 50c was modified.

Fixes: f2d1c4ee463 ("LU-14647 flr: mmap write/punch does not stale other mirrors")

Test-Parameters: env=ONLY="50c" serverversion=2.12.6-ddn42 \
testlist=sanity-flr
Test-Parameters: trivial env=ONLY="50c" testlist=sanity-flr

Signed-off-by: Alena Nikitenko <anikitenko@ddn.com>
Change-Id: Ia210c88586827bf8a9289cd6f9dd96c5e0cdc319
Reviewed-on: https://review.whamcloud.com/46440
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>