Use a specific envvar instead of TESTING

We should use fine-grained environment variables instead of general ones
like "TESTING."
check Heroku environment before deploying
Merge pull request #2553 from gittip/env-check

Check Heroku environment before deploying
Merge pull request #2497 from gittip/specific-envvar

Use a specific envvar instead of TESTING
run DB checks separately from homepage updates