Bug fix of the imagemanager module.
Bug fix of the imagemanager module.

This bug fix permits to:
* have the image downloaded from nginx endpoint working
* have additional debug string
* deal with the case when the cloudkeeper user is not member of the project
* deal with all non-string type of the appliance
The code has also been verified with pylint.

Pansanel/cloudkeeper-os,Mamut3D-docker/cloudkeeper-os