Prep $PROJECT and upper constraints for install

Before we can start enforcing constraints during tox runs we need to
ensure that the upper constraints from the requirements repo is in place
and up to date with the correct ref which may be latest $BRANCH or
$ZUUL_REF. Use zuul-cloner to ensure the state of both the project under
test and the constraints from the requirements repo.

To make use of this projects can update their tox targets to look for an
upper constraints file in the root dir of the project and have pip honor
those constraints when present.

Change-Id: I2829ba1bb0ce22b0f18080a1dc4ca7b1c77ce0e3

jenkins/jobs/experimental-workers.yaml

@@ -7,7 +7,7 @@
       - timestamps
 
     builders:
-      - zuul-git-prep
+      - zuul-git-prep-upper-constraints
       - install-distro-packages
       - mysql-prep
       - pgsql-prep

jenkins/jobs/macros.yaml

@@ -39,6 +39,28 @@
           /usr/zuul-env/bin/zuul-cloner -m $CLONEMAP --cache-dir /opt/git \
               git://git.openstack.org $ZUUL_PROJECT
 
+- builder:
+    name: zuul-git-prep-upper-constraints
+    builders:
+      - shell: |
+          #!/bin/bash -xe
+          CLONEMAP=`mktemp`
+          REQS_DIR=`mktemp -d`
+          function cleanup {
+              rm -rf $CLONEMAP $REQS_DIR
+          }
+          trap cleanup EXIT
+          cat > $CLONEMAP << EOF
+          clonemap:
+            - name: $ZUUL_PROJECT
+              dest: .
+            - name: openstack/requirements
+              dest: $REQS_DIR
+          EOF
+          /usr/zuul-env/bin/zuul-cloner -m $CLONEMAP --cache-dir /opt/git \
+              git://git.openstack.org $ZUUL_PROJECT openstack/requirements
+          cp $REQS_DIR/upper-constraints.txt ./
+
 - builder:
     name: zuul-git-branch-prep
     builders: