OpenSCAP 1.2.x will have different error messages

Addressing:
  1) Failure:
TestSession#test_session_new_bad
[/home/slukasik-f16/data/.hidden/workspace/ruby/ruby-openscap/test/xccdf/session_test.rb:24]:
Message was: failed to load external entity "" [oscap_source.c:151]
Unable to parse XML at: '' [oscap_source.c:152]