TST: Fix test_generate_run_xml

The tests were failing because the __init__.py was being referred to as
a local file instead of an absolute path that exists in the test_data
folder.

I've added a note about not changing this file without fixing the test
in test_ebi.py
Merge branch 'ebi-issue-314' of github.com:adamrp/qiita into ebi-issue-314