LU-15612 tests: Replace unicode double quotes

LU-15612 tests: Replace unicode double quotes

Under conf-sanity.sh replace unicode double
quotes with ASCII. This was exposed using
shellcheck.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In lustre/tests/conf-sanity.sh line 335:
umount_client $MOUNT -f || error ...
^-- SC1015: This is a unicode double quote. Delete and retype it.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Test-Parameters: trivial testlist=conf-sanity
Change-Id: I89e510a1d16059079378fc9399c1377017870477
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-on: https://review.whamcloud.com/46687
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>