lack of required extensions should be fatal

[Armando Migliaccio]

The extension framework has the ability to describe which extension depends on which, and if the requirements are not met it's hard to see how the server could work correctly.

[1] https://github.com/openstack/neutron/blob/master/neutron/api/extensions.py#L443

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/273140

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/273705

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/273705
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=5ccfbb5b2528fd1f9bd57a31b2784a5ed4107dac
Submitter: Jenkins
Branch: master

commit 5ccfbb5b2528fd1f9bd57a31b2784a5ed4107dac
Author: armando-migliaccio <email address hidden>
Date: Thu Jan 28 10:31:36 2016 -0800

    Fix required extensions mix-up

    These features have their required extensions mixed up. There is
    no reason why subnet pools (a core extension) depends on a non
    core extension like router. On the other end, DNS does indeed
    depends on it.

    Related-bug: #1538623

    Change-Id: If7e3566159919f1178373e3425310d457983f8ac

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/273140
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=b14c06b5eda188a665ca37f884e9591cd8d47535
Submitter: Jenkins
Branch: master

commit b14c06b5eda188a665ca37f884e9591cd8d47535
Author: armando-migliaccio <email address hidden>
Date: Wed Jan 27 08:23:48 2016 -0800

    Fail if required extensions are missing

    If the required extensions are missing, we currently log an error
    that is going to be practically ignored. That said, the unfulfilled
    requirement will most definitely going to lead to other failures,
    so we might as well fail fast.

    This patch also cleans up some <barf>dns-integration nonsense</barf>
    within the ML2 framework: the extension must not be declared statically
    as it's being loaded by the extension manager, and this fixes the lousy
    unit tests we have to live with. As for the db base plugin, some cleanup
    is still overdue, but it will have to be taken care of in a follow-up
    patch.

    Closes-bug: #1538623

    Change-Id: Id50eeb52c5d209170042b48821a29af3421c2f5c