Properly set the roundcube database password

After much trial and error, this should properly set the "roundcube" database password to "testPassword" when running these playbooks within vagrant.   Previously, what I think was happening, was when dbconfig-common gets installed, it generates a random password for roundcube and sets it within postgres.  So when the handler to add the carddav database tables was attempted to be executed, it would fail.

This now properly sets the roundcube database password to {{ webmail_db_password }}