Make remote API unit tests easier to read and write

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Update dns and volumes-from docs
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #5104 from crosbymichael/update-dns-vf-docs

Update dns and volumes-from docs
Merge pull request #5102 from shykes/api-cleanup-tests

Make remote API unit tests easier to read and write