[Grafana] Add openstack-tox-lower-constraints to neutron dashboard
[Grafana] Add openstack-tox-lower-constraints to neutron dashboard

Patch [1] added openstack-tox-lower-constraints job to Neutron's
gate and check queues.
This patch adds results of this job to Neutron failure rates grafana
dashboard.

[1] https://review.openstack.org/#/c/555939/

Change-Id: Ib5985d35c6f33cf93b163f73965ee992fffe0a66

openstack-infra/project-config,openstack-infra/project-config