Fix testing.ini not found when using cnxarchive-initialize_db

The initialize db script imports testing which tries to set up the test
environment.  If it's run outside test context, for example:

`python setup.py install`

`initialize_cnx-archive_db --with-example-data development.ini`

You'll get the following error:

IOError: [Errno 2] No such file or directory:
'/usr/local/lib/python2.7/dist-packages/cnx_archive-0.1-py2.7.egg/testing.ini'
Merge pull request #257 from Connexions/fix-initialize-db

Fix testing.ini not found when using cnxarchive-initialize_db