src-cli: long-running containers are not killed when hitting Ctrl-C

Created by: mrnugget

A customer reports that even after https://github.com/sourcegraph/src-cli/pull/369 long running steps are not killed by Ctrl-C:

Other small nitpick: there doesn’t seem to be a clean way to stop a long running src campaign command once it has started. The best method I’ve found so far is: ctrl-Z kill %1 Restart Docker