Issue 247: Add support for $HOME/.docker/config.json

[tourea]

As described in issue #247, docker-java, up to version 3.0.6, hardcoded the private registry authentication file to use ($HOME/.docker/.dockercfg).
I updated docker-java to support both config.json and .dockercfg (docker-java/docker-java#756), which has been released in version 3.0.7.

This commit upgrades docker-java's version to 3.0.7

[tourea]

@rnorth Please review

[bsideup]

Hey @tourea,
thanks for your PR. I'll take it :)

Looks like the Travis build is red, I restarted it, maybe some flaky test.

Meanwhile, did you run the tests locally?

[rnorth]

😄 it's nice to get this feature with a one-line change! As @bsideup says, it'll be good to get confirmation of no regressions once the tests have run.

Would it be worth adding an automated test for this, in case we somehow break it in the future?

BTW I think I also want to get my head around how this change might affect:

• the docker daemon discovery code in DockerClientFactory - are there any cases where this can now do the wrong thing?
• other features that run docker tools inside a container, e.g. docker-compose and upcoming dind. I suspect these won't work as expected out-of-the-box in conjunction with this, so do we need to update these to volume mount the config file or something similar?

[bsideup]

I see testExecInContainer test is still failing.

Did they change anything in docker-java related to execCmd?

[rnorth]

I've restarted the Travis build, as this seems to be passing locally for me (Docker for Mac 1.13.0)...

[bsideup]

LGTM