Support AWS using Libcloud or botocore. Refs #303.

* Renamed the current AWS cloud module to `libcloud_aws`.
* Created `botocore_aws` cloud module.
* Moved specific `botocore` functions to the `botocore_aws`.
* Minor PEP-8 and formatting.
Fix `SyntaxWarning: import * only allowed at module level`.
Remove `botocore` from the requirements file.
Merge pull request #341 from s0undt3ch/features/libcloud-and-botocore-aws

Support AWS using Libcloud or botocore. Refs #303.