Add docs for compute capabilities as traits
Add docs for compute capabilities as traits

Change I15364d37fb7426f4eec00ca4eaf99bec50e964b6 added the
ability for the compute service to report a subset of driver
capabilities as standard COMPUTE_* traits on the compute node
resource provider.

This adds administrator documentation to the scheduler docs
about the feature and how it could be used with flavors. There
are also some rules and semantic behavior around how these traits
work so that is also documented.

Note that for cases #3 and #4 in the "Rules" section the
update_available_resource periodic task in the compute service
may add the compute-owned traits again automatically but it
depends on the [compute]/resource_provider_association_refresh
configuration option, which if set to 0 will disable that auto
refresh and a restart or SIGHUP is required. To avoid confusion
in these docs, I have opted to omit the mention of that option
and just document the action that will work regardless of
configuration which is to restart or SIGHUP the compute service.

Change-Id: Iaeec92e0b25956b0d95754ce85c68c2d82c4a7f1

mahak/nova,klmitch/nova,rahulunair/nova,openstack/nova,klmitch/nova,klmitch/nova,mahak/nova,rahulunair/nova,rahulunair/nova,openstack/nova,openstack/nova,mahak/nova,klmitch/nova