selftest: run smbcacls test against a share with a DFS link

selftest: run smbcacls test against a share with a DFS link

The commit creates a dfs link in existing 'fileserver' env
share msdfs_share. Additionally we create a new dfs target in
a new share (with associated directory)

Additionally add a known fail as smbcacls doesn't not yet navigate DFS links.
A subsequent commit will fix smcacls to handle DFS (and remove the
knownfail)

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Jeremy Allison <jra@samba.org>