Fix usage of pip when non-root on Debian systems

[u1f35c]

pip defaults to user mode when non-root on Debian systems, causing an
error when building haaska.zip. Add --system to force system mode and
enable building as a regular user.

[anthonylavado]

Looks like this was proposed in the original Haaska, but due to concerns, it wasn’t implemented: auchter/haaska#70

[u1f35c]

Well that's annoying. Respun with a check to see if we have /etc/debian_version, which should mean we only add --system for anything based on Debian.

[anthonylavado]

@u1f35c Thanks for that update. I haven’t looked in the root issue much, but apparently it’s the source of some debate.

@mike-grant LGTM here. Merge?

[duckpuppy]

Actually... I'm building this on Debian Stretch, and I get the no such option: --system error referenced in #52 without using docker to build, just simply using make deploy.

pip install --help indeed shows --user, but no --system. This is from pip 18.0

If I edit the Makefile and remove all the extra detection logic for debian, I can build just fine as a normal user.