selftest: disable SMB encryption in simpleserver environment

selftest: disable SMB encryption in simpleserver environment

Encryption is currently not tested in this env so we can safely turn it
off. The next commit will add a blackbox tests that test combinations of
having encryption globally turned off and enabled (desired/required) on
a share.

This also adds a new share "enc_desired" with "smb encrypt = desired"
which will be used by the test in the next commit.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12520

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>