backend: add a convenience globals
Those globals are making our life easier becase now we can just stuff
like:
from copr_backend.setup import app, config, log
app.redirect_to_redis_log("actions") # creates actions.log
log.info("results are in %s", config.destdir)
So all the heavy-lifting related to redis logging, backend config
parsing, etc. is now for free. This is similar concept used by Flask on
the Frontend side.