more flexibility on image config

[remipichon]

• resource name for image config never actually had a sense if not to find the Dockerfile
• for both local and remote
  • if 'Dockerfile.' cannot be found, use the config.context where will be a 'Dockerfile'

==> this way, you can keep your Dockerfile name clean, relying only on the context

a few more tests to add

Doc to update

• your Dockerfile is named 'Dockerfile.'
  • image..json ==> VOC will look for 'Dockerfile.' and fail if not found
  • no matter the 'context' defined in configuration
• your Dockerfile is named 'Dockerfile' and you know where is it
  • image..json ==> instanceName is for logging purpose only
  • specify a 'context' where 'Dockerfile' is (mandatory)
  • we cannot put the 'context' in the filename as it could contain a path

[remipichon]

nope !