LU-15358 tests: Escape quote symbols in sanityn test 26b

LU-15358 tests: Escape quote symbols in sanityn test 26b

Shellcheck highlights that those quotes are actually unquoting
the variables. And looking at prior code we really try to ensure
you can tell which one is which even when some of them are empty
or have spaces.

Test-Parameters: trivial
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Change-Id: I2cdd0dcc1bce59b397f928cffeb790c74d8dc311
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59444
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>