docker scan does not handle Ctrl-C

[gtardif]

No description provided.

[gtardif]

@thaJeztah I could not reproduce this, did you actually Ctrl-C in a terminal or was it sending a kill signal to the docker scan invocation ?
I think sending a kill signal, the docker-cli will not propagate the signal to CLI plugins, but in a terminal, Ctrl-C will send the signal to processes in the same process group, therefore also cancelling the cli plugin execution.
To handling the kill signal we need a fix in docker/cli on CLI plugins in order to forward signals to child processes (I'd like to issue a PR when I have time on this).

[gtardif]

Actually I can reproduce (only on linux, behaviour is different on mac/win).