Install zuul-env venv with puppet

We need the zuul-env venv to be on all slaves not just dib/nodepool
built slaves. Do this by puppeting the virtualenv setup and pip install
of zuul in slave_common.pp.

Change-Id: I290a695c697fb456bee6f8212ba50b6c1b4533fc

modules/openstack_project/files/zuul-env-reqs.txt

@@ -0,0 +1 @@
+-e git+https://git.openstack.org/openstack-infra/zuul#egg=zuul

modules/openstack_project/manifests/slave_common.pp

@@ -108,4 +108,21 @@ class openstack_project::slave_common(
   package { $header_packages:
     ensure => present
   }
+
+  file { '/etc/zuul-env-reqs.txt':
+    ensure => present,
+    owner  => 'root',
+    group  => 'root',
+    mode   => '0444',
+    source => 'puppet:///modules/openstack_project/zuul-env-reqs.txt',
+  }
+
+  python::virtualenv { '/usr/zuul-env':
+    ensure       => present,
+    requirements => '/etc/zuul-env-reqs.txt',
+    owner        => 'root',
+    group        => 'root',
+    timeout      => 0,
+    require      => File['/etc/zuul-env-reqs.txt'],
+  }
 }