bug 1205783 - support the ldap user_enabled_invert parameter

[richm]

puppet-keystone master has support for this, but not the juno branch

[cwolferh]

@richm , total nitpick but please update your commit message to follow a format like https://github.com/jguiditta/astapor/commit/f1428b1f7cb6dba42dd2018940a47d9566520964 (note there is a blank line between the first "BZ #..." line and the http:// link).