Config manager

The path introduces the CloudConfigManager class, intended for easy conversion
between python dictionary and configuration text file formats. The class also
containing the defaults values for the cloud config hardcoded.

CloudConfigManager inherits from the abstract ConfigManager; that's done
in assumption that later another ConfigManager, namely TestConfigManager class
will be developed.

Blueprint test-engine

Change-Id: I8ea61f18cedd6d586a6e9cf8ae73a34edabf4bb9