Add automated tests

[mjordan]

Since Datastream CRUD writes to a repository, we should be using automated tests to make sure we aren't introducing any regression bugs.

• islandora_datastream_crud_push_datastreams
• islandora_datastream_crud_delete_datastreams
• islandora_datastream_crud_generate_derivatives

The challenge will be to provide tests for all of the options available for these commands.

.travis.yml and installing the Islandora stack are already in place.

[mjordan]

Basic tests for pushing new datastreams added.

[mjordan]

Up next, tests for islandora_datastream_crud_push_datastreams:

• --datastreams_mimetype
• --datastreams_label
• --update_object_label
• --update_dc
• --datastreams_revert