Gate requirements on ability to install deps.

Gate openstack/requirements on its ability to install the requirements
it specifies. This will help ensure that the mirror scripts can use this
repository to seed the mirror(s).

Change-Id: I5647a0ca32fd141c94a7e6afce1759fb1ad34442
Reviewed-on: https://review.openstack.org/23751
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins

modules/openstack_project/files/jenkins_job_builder/config/requirements.yaml

@@ -0,0 +1,21 @@
+- job:
+    name: gate-requirements-install
+    node: precise
+
+    triggers:
+      - zuul
+
+    builders:
+      - gerrit-git-prep
+      - shell: |
+          #!/bin/bash -xe
+          /usr/local/jenkins/slave_scripts/select-mirror.sh openstack requirements
+          virtualenv --clear --distribute .venv
+          # Ignore lines beginning with https?:// just as the mirror script does.
+          sed -e '/https\?:\/\//d' tools/pip-requires > tools/pip-requires.clean
+          sed -e '/https\?:\/\//d' tools/test-requires > tools/test-requires.clean
+          # Run the same basic pip command that the mirror script runs.
+          .venv/bin/pip install -M -U --exists-action=w -r tools/pip-requires.clean -r tools/test-requires.clean
+
+    publishers:
+      - console-log

modules/openstack_project/files/zuul/layout.yaml

@@ -841,9 +841,9 @@ projects:
 
   - name: openstack/requirements
     check:
-      - gate-noop
+      - gate-requirements-install
     gate:
-      - gate-noop
+      - gate-requirements-install
     post:
       - periodic-mirror-python26
       - periodic-mirror-python27