Print environment variables as first step in each job

[whimboo]

To make debugging easier we should print all the environment variables in each job.

[davehunt]

How can we make this a cross-platform build step?

[whimboo]

set should be available through mozmill-env across all platforms. printenv would be better but only seems to work on mac and linux. So we could use set as fallback.

[whimboo]

We may not have to print it as first step in the job but have those printed at all. Thanks to @davehunt who pointed me to https://wiki.jenkins-ci.org/display/JENKINS/EnvInject+Plugin which is doing that at th end of the build.

[davehunt]

This has been deployed to staging.

[davehunt]

I just encountered JENKINS-17688 locally, which means we may be unable to see injected environment variables after a restart of Jenkins for any old jobs.

[whimboo]

That's not pretty but should be ok for our kind of usage. We don't restart Jenkins that often.

[whimboo]

This is live on production now.