chore(tests): update vendored Docker cli code to v1.1.1
fix(tests): use `docker run --rm` instead of explicitly removing containers
fix(tests): report errors from `docker pull` on main goroutine

See http://golang.org/pkg/testing/#T.FailNow
Merge pull request #1268 from deis/component-tests-fixes

fix(tests): improve reliability and error reporting for component tests