Pass docker-args-build to apt "docker run"

[scjody]

This passes docker-args-build to the docker run commands used to run apt commands. This solves an issue seen at Plotly.

Note that we don't currently call the new docker-args-process-build because IMAGE_TAG isn't available to us. It also appears to be unavailable in dokku's builder-build so I'm unsure how the new trigger is supposed to work. Since Plotly uses only the older docker-args-build, this is fine for us.

This is currently untested but I'll update this PR when I've had the chance to test it on an internal Plotly system.

@josegonzalez FYI

[josegonzalez]

Yeah this seems reasonable.

Also the docker-args-process-build missing the IMAGE_TAG argument is a definite bug in Dokku, though I can revisit that in a future release.

Bump me once this passes and I'll merge to master/release.

[scjody]

This has passed my testing. (Docker arguments generated by an internal Plotly plugin are successfully passed to the container that runs apt.)

[josegonzalez]

Released as a patch in 0.9.7 as this is definitely a bug in my mind.

[scjody]

Thanks for the release!