Allow running gate lint and docs checks to run in virtual environments as non-root

[Nolan Brubaker]

Right now, the scripts/gate-check-lint.sh and scripts/gate-check-docs.sh files rely on the scripts/script-library.sh file, which does a check for the root user when sourced.

This isn't a major problem on the actual gating host, but when running the checks locally before pushing commits, it does get annoying.

Neither linting nor doc building should require running as root, though they should run in a virtual environment if not.

I can see a number of ways of addressing this, but I'm not sure which one is best. It's possible it could be a combination.

1 - Factor out any root-specific work to another script so that jobs that do need root can use it; those that don't can then source the script library just fine.
2 - Alter each script to provide it's own user ID checking (which seems redundant)
3 - Always run lint and gate checking jobs in virtualenvs, regardless of what user we're using

We should also look into how other OpenStack projects do this; I thinks there is a run-test.sh convention we may be able to adopt.

[Jesse Pretorius (jesse-pretorius)]

Some work has been done to implement tox based lint checks. Once they're fully working I'd like to switch over to using the standard template pep8 and bashate checks from -infra and entirely do away with our gate-check-lint script.

[Jesse Pretorius (jesse-pretorius)]

master review for the tox-base tests: https://review.openstack.org/216170

[Jesse Pretorius (jesse-pretorius)]

tox-based checks for these have now merged