Fix use_ssl behaviour for the validator and new puppetdb_disable_ssl parameter

Previously the defined check wasn't working as expected, this patches fixes
this by relying on the check for the `puppetdb` class instead.

Tests have been added, and the README has been updated to include the new
puppetdb_disable_ssl parameter for the `puppetdb::master::config` class.
Merge branch 'validator_ssl'

* validator_ssl:
  Fix use_ssl behaviour for the validator and new puppetdb_disable_ssl parameter