* Adds periodic task to purge node_history entries based upon
provided configuration.
* Adds recording of node history entries for errors in the
core conductor code.
* Also changes the rescue abort behavior to remove the notice
from being recorded as an error, as this is a likely bug in
behavior for any process or service evaluating the node
last_error field.
* Makes use of a semi-free form event_type field to help
provide some additional context into what is going on and
why. For example if deployments are repeatedly failing,
then perhaps it is a configuration issue, as opposed to
a general failure. If a conductor has no resources, then
the failure, in theory would point back to the conductor
itself.
Story: 2002980
Task: 42960
Change-Id: Ibfa8ac4878cacd98a43dd4424f6d53021ad91166
d17749249c