mount: move MS_{PROPAGATION,BIND,MOVE} detection

mount: move MS_{PROPAGATION,BIND,MOVE} detection

The previous commit does not properly fix the problem with "none"
fstype and MS_{PROPAGATION,BIND,MOVE} flags. The real fstype has to
be replaced with "none" before we try to use /sbin/mount.<type>
helper.

Old version:

	# grep test /proc/self/mountinfo
	16 18 0:19 / /mnt/test rw,relatime - tmpfs tmpfs rw

	# ./mount -v -v -v --make-private /mnt/test
	mount: fstab path: "/etc/fstab"
	mount: mtab path:  "/etc/mtab"
	mount: lock path:  "/etc/mtab~"
	mount: temp path:  "/etc/mtab.tmp"
	mount: UID:        0
	mount: eUID:       0
	mount: spec:  "tmpfs"
	mount: node:  "/mnt/test"
	mount: types: "tmpfs"
	mount: opts:  "rw"
	mount: external mount: argv[0] = "/sbin/mount.tmpfs"
	mount: external mount: argv[1] = "tmpfs"
	mount: external mount: argv[2] = "/mnt/test"
	mount: external mount: argv[3] = "-v"
	mount: external mount: argv[4] = "-o"
	mount: external mount: argv[5] = "rw"
	tmpfs on /mnt/test type tmpfs (rw)

	# grep test /proc/self/mountinfo
	16 18 0:19 / /mnt/test rw,relatime - tmpfs tmpfs rw
	17 16 0:20 / /mnt/test rw,relatime - tmpfs tmpfs rw

Fixed version:

	# grep test /proc/self/mountinfo
	16 18 0:19 / /mnt/test rw,relatime - tmpfs tmpfs rw

	# ./mount -v -v -v --make-private /mnt/test
	mount: fstab path: "/etc/fstab"
	mount: mtab path:  "/etc/mtab"
	mount: lock path:  "/etc/mtab~"
	mount: temp path:  "/etc/mtab.tmp"
	mount: UID:        0
	mount: eUID:       0
	mount: spec:  "tmpfs"
	mount: node:  "/mnt/test"
	mount: types: "tmpfs"
	mount: opts:  "rw"
	mount: mount(2) syscall: source: "tmpfs", target: "/mnt/test",
	filesystemtype: "none", mountflags: 262144, data: (null)

	# grep test /proc/self/mountinfo
	16 18 0:19 / /mnt/test rw,relatime - tmpfs tmpfs rw

Signed-off-by: Karel Zak <kzak@redhat.com>