Switch from debian-jessie to debian-stable (stretch)

Now that we have debian-stretch images online for openstack-infra,
we'd like to remove debian-jessie[1]. This updates zuul jobs to use the
debian-stable label, which happens to now be debian-stretch.

[1] http://lists.openstack.org/pipermail/openstack-dev/2018-April/129573.html

Change-Id: I7ea475bbdcde533dfde0a30bb516a5fe3a83cab7
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

zuul.d/jobs.yaml

@@ -14,9 +14,9 @@
 # limitations under the License.
 
 - job:
-    name: openstack-ansible-functional-debian-jessie
+    name: openstack-ansible-functional-debian-stable
     parent: openstack-ansible-functional
-    nodeset: debian-jessie
+    nodeset: debian-stable
 
 - job:
     name: openstack-ansible-functional-fedora-27

zuul.d/project.yaml

@@ -17,7 +17,7 @@
       jobs:
         - openstack-ansible-linters
         - openstack-ansible-functional-centos-7
-        - openstack-ansible-functional-debian-jessie
+        - openstack-ansible-functional-debian-stable
         - openstack-ansible-functional-fedora-27
         - openstack-ansible-functional-opensuse-423
         - openstack-ansible-functional-ubuntu-xenial
@@ -28,7 +28,7 @@
       jobs:
         - openstack-ansible-linters
         - openstack-ansible-functional-centos-7
-        - openstack-ansible-functional-debian-jessie
+        - openstack-ansible-functional-debian-stable
         - openstack-ansible-functional-fedora-27
         - openstack-ansible-functional-opensuse-423
         - openstack-ansible-functional-ubuntu-xenial