Revert unnecessary `$default_ssl_vhost` validation change.

The `validate_bool()` call was moved in
112437730f70e18daf3aed9cedffd0c46348204d making it FreeBSD centric, but
it should be validated outside of any other condition.
Fix spec test for `default_ssl_vhost  => true`

The spec test for `default_ssl_vhost  => true` was retesting the test
for `default_vhost  => true` instead.