Added EC2 support to Management Systems

Specific changes:
- Added EC2System as a new mgmt_system
- Added EC2System support to setup_mgmt_system fixture
- Removed two returns that could never get called
- Added boto to requirements
- Stripped trailing whitespace where needed
- minor PEP8ness where needed
- Changed inconsistent double/single quote usage to be all single
Added a new server_roles fixture

- Uses decorators to pass required roles into the fixture (see docstring on the fixture)
- fixes #40
- refs #48
Merge pull request #47 from seandst/add-ec2-mgmt-system

Added EC2 support to Management Systems
Merge pull request #51 from seandst/add-roles-fixture

Added a new server_roles fixture