Clean up some messy stack traces

[baronfel]

There are a few scenarios where we don't exit cleanly here:

• cancelling the build - TaskCanceledException: A task was canceled. hitting ctrl-c during container create sdk#36593
• httpclient timeouts - error CONTAINER1013: Failed to push to the output registry: The request was canceled due to the configured HttpClient.Timeout of 100 seconds elapsing....

We should provide better handling for these two scenarios, and we should provide a configuration knob for the HTTP timeout - something like SDK_CONTAINER_HTTP_TIMEOUT_SECONDS to allow users to override this. When we add it we should make sure the error message for HttpClient timeouts calls out the new environment variable.

[baronfel]

We've done the first part of this in 8.0.200, and the second part is captured in #543, so closing this issue.