Skip tomcat error tests when lxml is unavailable

Until _scrap_response has a Tomcat path which doesn't depend on
lxml.html there's no point in running these tests on a different config
Tests: expect content extraction to fail

Once https://github.com/toastdriven/pysolr/issues/90 is fixed we can
re-enable this test
Tests: update test_full_url for multi-core config