The big mechanical change here is to NOT store `t` as a field on
the `CLI` object (which has been renamed as well to fix the odd
capitalization). The way the tests are structured meant that the
"subtests" were using the _parent_ `*testing.T` instance, which
causes various oddities including confusing messages on failure
about a child test causing a panic in the parent.
Additionally, a few tests have been blocked from running in
parallel because they are sharing `compose.yaml` fixtures and
can fail as a result (e.g. due to a port conflict on the host).
I'll fix these in follow-up PRs but want to focus on correctness
for the tests before optimizing them.
Signed-off-by: Milas Bowman <milas.bowman@docker.com>