Replace pipes.quote by shlex.quote when Py3

[kinow]

We have from pipes import quote in a few parts of the code. But the pipes module exports in __all__ only Template. The quote method was supposed to be internal, but probably due to it being useful, now it is exported/documented in shlex.quote, but I believe it's Py3 only

So when moving to Py3, 2to3/six/futurize won't alert us about that, and so this ticket as a remainder 😬

[kinow]

Found this while reviewing #2809 and finding the pipes.quote usage, which was new for me 🤓

[oliver-sanders]

Python unhelpfully deprecated pipes.quote in 2.7 but diddn't expose it again until 3.3!

[kinow]

Had no idea that that's what happened hahaha. Bet they got a few angry users demanding a replacement