[RFE] Change config options to be mutable

[Ruby Loo]

SIGHUP support for ironic [1][2] will allow the ironic-api and ironic-conductor services to reload mutable configuration options. To start with, these configuration options are mutable:

  * ``[DEFAULT]/debug``
  * ``[DEFAULT]/log_config_append``
  * ``[DEFAULT]/pin_release_version``

This RFE will make most of the ironic configuration options mutable. The work can be done in one patch or a series of patches, but we should try to land them all in a short amount of time, and in the same named release so as not to confuse operators as to which options were made mutable and in which release.

The work involves:

  * deciding which options make sense to be mutable (they should be listed here in a comment, we probably shouldn't approve this w/o an idea of what those options are
  * making sure those option values are not cached

[1] RFE/bug: https://bugs.launchpad.net/ironic/+bug/1585595
[2] specification: http://specs.openstack.org/openstack/ironic-specs/specs/approved/sighup_on_ironic_services.html

[Julia Kreger (juliaashleykreger)]

Pin release version is mutable and is in ironic.

The other two noted options are not in ironic, they come from oslo.log.

It is worth noting many options are already mutable, so largely it seems like the work for this has already been done, just not the actual tracking to close out this item. Moving to fix released.