Refines and tests collection create/update/delete commands

[flyingzumwalt]

Replaces #14, which was submitted from my master branch. Submitting from a feature branch instead.

1. Builds out collection create/update/delete commands
2. Adds test coverage for these and related commands (requires starting solr. It's slow, but you know -- now the code has tests)
3. Moves basic_configs fixtues into basic_configs/config so that you can actually use them to create a working core (which is used by the tests to create/update collections)
4. Adds a little bit of error handling

[flyingzumwalt]

Note: These changes are included in #17