Dedicated test for get_7z()

[mih]

Mac is not happy: #96

[adswa]

I've restarted the mac worker for remote debugging

[adswa]

something is odd in the log of the job I've just restarted: "docker: command not found"

tools/ci/setup-sshd
tools/ci/setup-sshd: line 34: docker: command not found
Generating public/private rsa key pair.
Your identification has been saved in /Users/appveyor/.ssh/datalad_tests_id_rsa

I assume docker did work before on mac, right?

[adswa]

Ah, I found a comment in the PR that added the docker support (#52):

There is no Docker deployment available for appveyor Mac workers. An
attempt to deploy it manually has not yielded a reliably working
system with a sensible deployment cost. As a consequence, the Mac CI
runs will use SSH-access to "self" (the exact same worker environment
via a localhost SSH connection). This is not ideal, but an acceptable
compromise.