Add error details for failed container start: Fixes #215

[johnaohara]

When a container runtime reports an error when trying to start a container, the detail of the error is missing;

07:59:20.910 Running qDup version 0.8.2 @ 68705d4
07:59:20.911 output path = /tmp/qdup-debug
07:59:20.911 shell exit code checks enabled
07:59:21.074 json server listening at fedora:31337
07:59:22.497  failed to connect to LOCAL//registry.fedoraproject.org/f35/python3
07:59:22.498 setup failed to connect LOCAL//registry.fedoraproject.org/f35/python3
07:59:22.502 failed to connect all ssh sessions for setup

It would improve UX if the details of the error were logged so that a user can begin troubleshooting problems