Make pid file configurable

And some other fixups around starting the daemon:
* read config file before forking
* add '-d' option to avoid forking
* default pidfile to /var/run/elastic-recheck/elastic-recheck.pid
* add pidfile option to config file
* switch to python-daemon library (which is the version of the
  lib that the code was expecting anyway)
* use expanduser in the query file path (to match the rest of the
  paths)

Change-Id: I674778ef189cd216a80f74bd449cdc3b12b57a7d