Refactoring for Windows related utilities location

Moves all Windows related utilities in utils/windows
ConfigDrive metadata service refactoring

Minor refactoring to properly support multiple OSs.
Metadata test and metadata refactoring

Added mock based unit tests for maasservice module, baseopenstack
module and changed init module and httpservice module tests,
plugins with different imports due to utils location modiffied
and removed 3 unused imports from baseopenstack module