Close #506 Add test for RSS feed parser

Add a test that pulls different RSS feed attributes such as title,
speaker, etc. and compares it to a JSON file with the expected results.

test_get_presentations() checks attributes' title, speaker, level,
status, time, event, and room to see if they contain correct values.
Mark RSS feed parser test as expected to fail

This test will be run but no traceback will be reported when it fails.
Instead, terminal reporting will list it as "expected to fail".

Related to #555

http://pytest.org/latest/skipping.html#xfail