This test was just incorrect (and testing incorrect
behavior): it was checking that `docker run` exited with a `context
canceled` error after signalling the CLI/cancelling the command's
context, but this was incorrect (and was fixed in
991b1303da - which was when this test
started failing).
However, since this test assertion was happening inside of a goroutine,
it would sometimes pass if this assertion didn't get to run before the
test suite terminated. It was flaky because sometimes this assertion
inside the goroutine did get to execute, but after the test finished
execution, which is a big no-no.
As an aside, assertions inside goroutines are generally bad, and `govet`
even has a linter for this (but it only catches `t.Fatal` and `t.FailNow`
calls and not `assert.Xx`.
Signed-off-by: Laura Brehm <laurabrehm@hey.com>