Unable to influence atom scheduling priority

[Joshua Harlow]

Currently when there are multiple atoms that can be scheduled at the same time there is no way to define a ordering to the selection of atoms that can run at the same time. Typically it is useful to allow for a priority to be associated with an atom so that when it can be scheduled it will run in priority order (if a priority is defined in the first place).

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/210620
Committed: https://git.openstack.org/cgit/openstack/taskflow/commit/?id=70e58977c944d23f2133cd1b3d6f3970f101e7ab
Submitter: Jenkins
Branch: master

commit 70e58977c944d23f2133cd1b3d6f3970f101e7ab
Author: Joshua Harlow <email address hidden>
Date: Fri Aug 7 14:46:24 2015 -0700

    Add atom priority ability

    In situations where many atoms can execute at the same
    time it is sometimes useful to denote that when this situation
    happens that certain atoms should execute/revert before other
    atoms (or at least an attempt should be made to do this) instead
    of being nearly arbitrary.

    This adds a priority class attribute to the atom class (which
    can be overridden or changed as needed) which is then used in
    the runtime state machine to sort on so that atoms with higher
    priority get submitted (and therefore executed/reverted) first.

    Closes-Bug: #1507755

    Change-Id: I3dcc705959085cba167883c85278e394b5cb1d2b