Add tools/conf/check_uptodate to tox.ini

To ensure that our sample config file, etc/ironic/ironic.conf.sample,
does not get out of sync with the code, this patch introduces a check
to tox that will compare the proposed ironic.conf.sample to a
freshly generated one, and error if they are not identical.

Ported from Nova's tools/config/check_uptodate.sh script.

Change-Id: Ic2898142754547e32bc4c03d23eca5d6a33721fc
Closes-bug: 1255621