Extract custom resource classes from flavors

[OpenStack Infra]

https://review.openstack.org/473627
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/nova" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit 1dc93d00b0ea2d2be5c8a150b1336f2d56d71dff
Author: EdLeafe <email address hidden>
Date: Mon Jun 12 23:26:40 2017 +0000

    Extract custom resource classes from flavors

    This patch adds code to look in a flavor's extra_specs for keys
    beginning with "resources:", and if found, use them to update the
    resources dict sent to placement.

    The entry for a custom resource class will look like
    "resources:CUSTOM_FOO=1". Additionally, standard classes in a flavor can
    be overridden with an entry that looks like: "resources:VCPU=0". If a
    standard class is found in extra_specs, it will be used instead of the
    amount in the flavor. This is useful for things like Ironic, where an
    operator may want to list the amount of RAM, disk, etc. in the flavor,
    but use a custom Ironic resource class for doing the actual selection.
    An amount for a standard class that is zero will result in that class
    being removed from the requested resources dict sent to placement.

    DocImpact
    We should document the capability and rules in
    https://docs.openstack.org/admin-guide/compute-flavors.html#extra-specs.

    Blueprint: custom-resource-classes-in-flavors

    Change-Id: I84f403fe78e04dd1d099d7d0d1d2925df59e80e7

[jichenjc (jichenjc)]

https://review.openstack.org/#/c/472275/13/specs/pike/os-manuals-migration.rst

guess this should be done when the doc migration complete?