LU-14061 utils: prefer mounting with specified fstype

LU-14061 utils: prefer mounting with specified fstype

If the server filesystem is mounted with "-t lustre" use that type
for mounting instead of automatically selecting "lustre_tgt" for
server mounts, so that it is appearing in /proc/mounts correctly,
and "mount -t lustre" will list all of these filesystems.

Only if "mount -t lustre_tgt" is used will mount.lustre_tgt be called,
and that will internally use "lustre_tgt" as the filesystem type, and
only fall back to type "lustre" if that does not work.  This will give
userspace plenty of time to transition to using "lustre_tgt" for
server mountpoints.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ifd7560c800acdfe14c9564bbf955ecad1224f2e3
Reviewed-on: https://review.whamcloud.com/40474
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>