samba-tool: validate password early in `domain provision`

samba-tool: validate password early in `domain provision`

Checks password against default quality and length standards when it is entered,
allowing a second chance to enter one (if interactive), rather than running
through the provisioning process and bailing on an exception

Includes unit tests for the newly-added python wrapper of check_password_quality
plus black-box tests for the checks in samba-tool.

Breaks an openldap test which uses an invalid password.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=9710
BUG: https://bugzilla.samba.org/show_bug.cgi?id=12235

Signed-off-by: Jamie McClymont <jamiemcclymont@catalyst.net.nz>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>