Update tox.ini for new upper constraints strategy

The requirements team has defined a new strategy for handling
upper constraints[1]. This patch applies those strategies to
neutron-lbaas-dashboard.
This also pins the nodejs jobs to xenial.

[1] http://lists.openstack.org/pipermail/openstack-discuss/ \
    2019-May/006478.html

Change-Id: I970ff6a4f5cbb7ad1d2172285a5d84242e2c4ecf

.zuul.yaml

@@ -6,11 +6,13 @@
     check:
       jobs:
         - nodejs-npm-run-lint:
+            nodeset: ubuntu-xenial
             vars:
               node_version: 4
             required-projects:
               - openstack/horizon
         - nodejs-npm-run-test:
+            nodeset: ubuntu-xenial
             vars:
               node_version: 4
             required-projects:
@@ -18,11 +20,13 @@
     gate:
       jobs:
         - nodejs-npm-run-lint:
+            nodeset: ubuntu-xenial
             vars:
               node_version: 4
             required-projects:
               - openstack/horizon
         - nodejs-npm-run-test:
+            nodeset: ubuntu-xenial
             vars:
               node_version: 4
             required-projects:

tox.ini

@@ -5,7 +5,7 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt?h=stable/queens} {opts} {packages}
+install_command = pip install {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
    NOSE_WITH_OPENSTACK=1
@@ -15,7 +15,8 @@ setenv =
    NOSE_OPENSTACK_SHOW_ELAPSED=1
    CLIENT_NAME=neutron-lbaas-dashboard
    DJANGO_SETTINGS_MODULE=neutron_lbaas_dashboard.tests.settings
-deps = -r{toxinidir}/requirements.txt
+deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/queens}
+       -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
        http://tarballs.openstack.org/horizon/horizon-stable-queens.tar.gz
 whitelist_externals = npm