zfs_main.c: Cleanup

- `HELP_MOUNT` should accurately reflect the mount options
- Improved the "recursive" checks in `get_one_dataset()`
- Corrected the `zfs_open()` implementation
- Changed `-r` to `-A` since "recursive" may be misleading
- Added `mount_noauto` to enable the mounting of "recursive" filesystems

Signed-off-by: QORTEC <[email protected]>

man/man8/zfs-mount.8

@@ -81,10 +81,10 @@ See
 .Xr mount 8
 for more information.
 .It Fl a Ar filesystem
-Mounts the specified ZFS file system and its children.
+Mounts the specified filesystem and its children, provided they are available.
 If no filesystem is specified, then all available ZFS file systems are mounted; may be invoked automatically as part of the boot process if configured.
-.It Fl r Ar filesystem
-Mounts the specified ZFS file system and its children.
+.It Fl A Ar filesystem
+Mounts the specified filesystem and its children, provided they are available.
 Note: datasets with the `canmount=noauto` property will also be mounted.
 .It Ar filesystem
 Mount the specified filesystem.