Lock sure to a working version for tests
[Block Device] Add support for using block device mappigns in launch configs
Add Block Device Mapping Support

* Adds Support for creating block device mappings on the command line
* Requires Boto Support for parsing Block Device Mappings (>=2.27.0)
* Requires Moto Support for storing, parsing, and returning Block Device Mappings (PR #102)
Update README
Cleanup README
Force moto for tests
Merge pull request #6 from andrewgross/feature/ephemeral-mounting

Feature/ephemeral mounting