snap does not remove br-ex on uninstall

[Pen Gale]

MicroStack leaves the bridge that ovs-ctl sets up (br-ex) in place on reinstall.

The bridge goes away after a reboot, but we should do a better job of cleaning up after ourselves.

(This can also cause bugs when performing several test cycles on a single machine.)

[Pen Gale (pengale)]

This one is tricky. We'd like to use ovs tools to tear down the bridge when the snap uninstalls. But the openvswitch service is no longer running by the time we're running the teardown hooks.

[OpenStack Infra (hudson-openstack)]

Change abandoned by Pete Vander Giessen (<email address hidden>) on branch: master
Review: https://review.opendev.org/693758
Reason: This needs more thought. Abandoning for now.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/695606

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/695606
Committed: https://git.openstack.org/cgit/x/microstack/commit/?id=a89f5574c3d6decac4a37f0c0969e6776ca072f3
Submitter: Zuul
Branch: master

commit a89f5574c3d6decac4a37f0c0969e6776ca072f3
Author: Pete Vander Giessen <email address hidden>
Date: Wed Nov 27 21:47:52 2019 +0000

    Added microstack.remove command

    Running microstack.remove will remove the br-ex virtual bridge device,
    then uninstall MicroStack.

    We do this because we can't use ovs-ctl to remove the bridge as part
    of a remove hook, as the Open vSwitch daemons are not running at that
    point. The microstack.remove command gives operators a way to cleanly
    uninstall the snap, without needing to reboot to get rid of br-ex.

    Added test exercising the code to test_basic.py.

    Rerranged entry points a bit (moved some things into main.py) to make
    code sharing easier, and to prevent a proliferation of entry point
    scripts in our root dir.

    Change-Id: I9ff25864cd96ada3a9b3da8992c2b33955eff0b4
    Closes-Bug: #1852147