$password_hash not being encrypted when sent to postgresql::database_user

Fixes #216 where $password_hash was not being encrypted which caused an ALTER ROLE to be run every time the puppet agent runs. Also Fixes puppetlabs/puppetlabs-puppetdb#72 downstream.

Because of this fix, the postgresql::db::password parameter MUST be passed in plain text. This may be undesirable for some/most. Perhaps there should be an option to either send the password as a hash as well as plain text, OR change the postgresql::db::password to postgresql::db::password_hash and require it to be sent as a hash.