Integration test insecure registry

The integrations tests use their own registry so avoid hitting docker
hub rate limits.

This was using a self signed certificate but instead use
`--insecure-registry` to let the docker daemon use HTTP.

test/integration/docker/shared/Dockerfile

@@ -10,8 +10,6 @@ RUN mkdir ssh && \
 COPY registry-dns.conf .
 COPY boot.sh .
 
-RUN mkdir certs && openssl req -newkey rsa:4096 -nodes -sha256 -keyout certs/domain.key   -x509 -days 365 -out certs/domain.crt   -subj '/CN=registry' -extensions EXT -config registry-dns.conf
-
 HEALTHCHECK --interval=1s CMD pgrep sleep
 
 CMD ["./boot.sh"]