previously in run_app_paas.sh, we captured stdout from the app and
piped that into the log file. However, this came up with a bunch of
problems, mainly:
* exceptions with stack traces often weren't formatted properly,
and kibana could not parse them
* celery logs were duplicated - we'd collect both the json logs and
the human readable stdout logs.
instead, with the updated utils library, we can use that to log json
straight to the appropriate directory directly.
in tests, we were replacing os.environ with a basic dict so that
we didn't overwrite the contents of the real environment during tests.
However, os.environ doesn't accept non-str values, so this commit
changes the fixture so that it asserts all values set are strings.
We needed to change how we store ip whitelist stuff in the env because
of this.
