Adles

Fixed
- Fixed bug where interfaces (and their dependencies) would be imported,
even if they were not being used. This caused the "pip install docker" error.

Changed
- Minor improvements to logging.

Added
- An interface for libvirt (LibvirtInterface).
- LibcloudInterface that is inherited by LibvirtInterface and CloudInterface.
- Libvirt to infrastructure-specification.
- libvirt to optional-requirements.

Changed
- Significant changes to class heirarachy. All interfaces now inherit from Interface and class its init method.
There is a separate PlatformInterface that has most of the functionality Interface did, and this is what is now called from main().
- Tweaked some boilerplate code in the interfaces.
- Updated parser.
- Formatting tweaks.
- Moved apache-libcloud to requirements.

Initial stab at cloud interface using Apache libcloud
(quickly superseded by 1.3.0, so ignore this version).