Bulk of updates for ironic-discoverd

* Use new configuration option from 0.2.0
* Rename units to match future ironic-discoverd RPM
* Port changes from PR #32:
  * Configure discovery parameters in answers file
  * Use configuration file instead of command-line parameters for dnsmasq
these 3 variables also need to be exported from scripts/instack-install-undercloud, around line 36 where the other vars from the answers file are exported.