RestEasyUriBuilder.host does not accept null to reset host per JavaDoc

The JavaDoc for UriBuilder.host states that "A null value will unset the host component of the URI",
however the ResteasyUriBuilder throws IllegalArgumentException "schemeSpecificPart was null" when host value is null.

This is useful to create a relative URI for the request.

The fix only changed the

    @Test
    public void shouldDeleteHostWhenSettingToNull() {
        UriBuilder builder = UriBuilder.fromUri("http://example.org/path");

        builder.host(null);

        assertEquals("http:/path", builder.build().toString());
    }