L3 agent cannot be manually scheduled

[Rodolfo Alonso]

This bug is similar to https://bugs.launchpad.net/neutron/+bug/1883513.

When a new L3 agent is manually scheduled, "L3AgentSchedulerDbMixin.get_vacant_binding_index" should always provide a vacant index, even if this index exceeds the maximum number of configured L3 agents. That means, when "is_manual_scheduling=True", a valid vacant index number should be provided.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/737736

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/ussuri
Review: https://review.opendev.org/738179

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/737736
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=2bb514f2d73a64b6f954990a2ff12f5baa3a97cd
Submitter: Zuul
Branch: master

commit 2bb514f2d73a64b6f954990a2ff12f5baa3a97cd
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Wed Jun 24 09:58:09 2020 +0000

    L3 agent scheduler should return a valid index if manual scheduling

    When retrieving a vacant L3 agent binding index, if
    "is_manual_scheduling" is set, the method "get_vacant_binding_index"
    should always return a valid binding index. If the existing binding
    indexes are sequentially aligned, the method will return a new one
    on top; if there is a gap in the binding indexes list, the first
    free index will be returned.

    Closes-Bug: #1884906

    Change-Id: I0a89bca0734d3e735fb357e488f85589e81d709f

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/738179
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=5f8af42dbdf4686936e05a07d9ead9c9e600b8eb
Submitter: Zuul
Branch: stable/ussuri

commit 5f8af42dbdf4686936e05a07d9ead9c9e600b8eb
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Wed Jun 24 09:58:09 2020 +0000

    L3 agent scheduler should return a valid index if manual scheduling

    When retrieving a vacant L3 agent binding index, if
    "is_manual_scheduling" is set, the method "get_vacant_binding_index"
    should always return a valid binding index. If the existing binding
    indexes are sequentially aligned, the method will return a new one
    on top; if there is a gap in the binding indexes list, the first
    free index will be returned.

    Closes-Bug: #1884906

    Change-Id: I0a89bca0734d3e735fb357e488f85589e81d709f
    (cherry picked from commit 2bb514f2d73a64b6f954990a2ff12f5baa3a97cd)