LU-14313 utils: mount error when no server support

LU-14313 utils: mount error when no server support

When the mount utility was built without server support,
and this causes the mount to fail, an error message should
say so.

The error values returned by main() should be positive as
they are exposed to the user.

Upon mount() failure, errno must be checked to determine
the reason for the failure.  The return value is -1.

Test-Parameters: trivial
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: I49906340f6ddbe16b7503663cedabe0085daf113
Reviewed-on: https://review.whamcloud.com/41182
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>