Make it possible to specify custom name for container_output

[goldmann]

It would be nice if we could specify a custom name (for example based on the test method) to quickly find the right container_output log.

[rwngwn]

I've implemented a way to put custom container name in output.
if you create container in a way like

c= Container(image_id=xxxxx, name='Test' )

and than specify

c.stop(mark_output=True)

it should create file like:
container_Test_xxx43403285932...._output.txt