LU-17156 tests: Improve zfs_or_rotational()

LU-17156 tests: Improve zfs_or_rotational()

Improve zfs_or_rotational() under test-framework.sh to handle
get_param failure gracefully and not throw bash syntax error.

Fix ostname_from_index() to print the OST name once instead of
twice if there are multiple mountpoints (e.g. sanityn).  If the
caller wants the specific name when there are two different
filesystems mounted, the specific mountpoint should be given.

Test-Parameters: trivial testlist=sanityn
Fixes: 43c3a804fe ("LU-13805 tests: Add racing tests of BIO, DIO")
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I0b914236865574dadd4ba0cb9a0ba7a7775fefc5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52973
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>