client: do not fallback to GET if HEAD on _ping fail to connect
When we see an `ECONNREFUSED` (or equivalent) from an attempted `HEAD` on the
`/_ping` endpoint there is no point in trying again with `GET` since the server
is not responding/available at all.
Once vendored into the cli this will partially mitigate https://github.com/docker/cli/issues/1739
("Docker commands take 1 minute to timeout if context endpoint is unreachable")
by cutting the effective timeout in half.
Signed-off-by: Ian Campbell <ijc@docker.com>
(cherry picked from commit 8c8457b0f2f85d58c0e1a5b4a0e174d7808cf886)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>