LU-14204 tests: use first available import

LU-14204 tests: use first available import

In test suite, be careful to use first available import in case there
are multiple mount points.

Test-Parameters: trivial
Test-Parameters: env=SHARED_KEY=true testlist=sanity
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Ib099cd5c9666e9d4faf9445846c91a225f4a8f57
Reviewed-on: https://review.whamcloud.com/42019
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>