this changes the behavior of hot containers:
1) we are no longer populating a hot container with all of the env vars from the
first request to start up that hot container. this will only populate the
container with any vars that are defined on the app or route.
2) when env vars are changed on the route or app, we will now start up a new
hot container that contains those changes.
3) fixes a bug where we could have a collision if the image and path name
created one, e.g. `/yo/foo` & `oze/yo:latest` collides with `/yo/fo` and
`ooze/yo:latest` (if all other fields are held constant), since we're
name spacing with app name in theory it would happen to the same user (though
we were relying on a comma delimiter there, not great). now we use NULL bytes
which should be hard to get in through a json api ;) i added a sha1 to keep
the size of the (soon to be very large) map down, i don't expect collisions
but, well, it's a hash function.
a small note that we could add a few things to the hot container that will not
change on a request basis, such as `app_name`, `format` and `route` but it's a
bit pedantic. ultimately, it's confusing imo that we have a different set of
vars in the env and in the request itself for hot, which is unavoidable unless
we choose to omit setting env vars entirely, but it seems to be what the
people want (lmk, people, if otherwise).
Each time when MQ becomes unreachable HTTP GET /tasks returned HTTP 500
and code was not handling this case except expecting networking errors.
After that it tried to unmarshal empty response body that caused another sort of an error.
This patch triggers error based on http response code, explicitly checking if response code
is something unexpected (not HTTP 200 OK).
Response status code for /tasks for changed from 202 Accepted to 200 OK according to swagger doc.
