Change nova docker tests to run in the main Ubuntu image.

We were having intermittent failures with the experimental fedora 20
image so we are going to switch to the more tested Ubuntu image.

Change-Id: I3261af31bb07f281ba5acfb083ff46bdaa043e6f

modules/openstack_project/files/jenkins_job_builder/config/nova-docker.yaml

@@ -1,6 +1,6 @@
 - job:
-    name: 'check-nova-docker-dsvm-f20'
-    node: 'devstack-f20'
+    name: 'check-nova-docker-dsvm'
+    node: 'devstack-precise || devstack-trusty'
 
     wrappers:
       - build-timeout:

modules/openstack_project/files/zuul/layout.yaml

@@ -662,7 +662,7 @@ jobs:
     voting: false
   - name: gate-oslo-incubator-python33
     branch: ^(?!stable/havana).*$
-  - name: check-nova-docker-dsvm-f20
+  - name: check-nova-docker-dsvm
     voting: false
   - name: check-neutron-dsvm-functional
     branch: ^(?!stable/havana).*$
@@ -1177,7 +1177,7 @@ projects:
       - name: python-jobs
       - name: check-requirements
     check:
-      - check-nova-docker-dsvm-f20
+      - check-nova-docker-dsvm
 
   - name: openstack/pycadf
     template: