Inline the test.docker.io fingerprint in the install.sh script as well

As long as we're doing it, we ought to do it for all the "official" Docker properties at least

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #3551 from tianon/test-docker-io-gpg-fingerprint

Inline the test.docker.io fingerprint in the install.sh script as well