Add a check in deploy.sh for environment variables

[rohitpaulk]

When deploying #4438, I forgot to add the CHECK_NPM_SYNC_EVERY env var, and gratipay.com was down for around 3 minutes until I figured out what was wrong and fix it.

We should be able to detect this before deploying by adding a check to deploy.sh

[chadwhitacre]

I really thought we already had a check for that. 🤔

[chadwhitacre]

Okay, hitting this (slack) while deploying #4305. Regression due to #4365. The -m gratipay.wireup is not actually being run, so it looked like it worked for purposes of #4365 but of course is failing to keep us safe from envvar change errors. Lessee here ...

[chadwhitacre]

Got it! PR forthcoming ...

[gratipay] $ ./env/bin/honcho run -e defaults.env,local.env ./env/bin/python -m gratipay.wireup
[gratipay] $ heroku config -s -a gratipay | ./env/bin/honcho run -e /dev/stdin ./env/bin/python -m gratipay.wireup
pid-79859 thread-140735204086528 (MainThread) ==========================================
pid-79859 thread-140735204086528 (MainThread) Oh no! Gratipay.com needs these missing 
pid-79859 thread-140735204086528 (MainThread) environment variables:
pid-79859 thread-140735204086528 (MainThread)  
pid-79859 thread-140735204086528 (MainThread)   PROJECT_REVIEW_REPO
pid-79859 thread-140735204086528 (MainThread)   PROJECT_REVIEW_TOKEN
pid-79859 thread-140735204086528 (MainThread)   PROJECT_REVIEW_USERNAME
pid-79859 thread-140735204086528 (MainThread)  
pid-79859 thread-140735204086528 (MainThread) (Sorry, we must've started looking for 
pid-79859 thread-140735204086528 (MainThread) these since you last updated Gratipay!)
pid-79859 thread-140735204086528 (MainThread)  
pid-79859 thread-140735204086528 (MainThread) Running Gratipay locally? Edit ./local.env.
pid-79859 thread-140735204086528 (MainThread) Running the test suite? Edit ./tests/env.
pid-79859 thread-140735204086528 (MainThread)  
pid-79859 thread-140735204086528 (MainThread) See ./default_local.env for hints.
pid-79859 thread-140735204086528 (MainThread) ==========================================
Missing envvars: PROJECT_REVIEW_REPO, PROJECT_REVIEW_TOKEN, PROJECT_REVIEW_USERNAME.
[gratipay] $