Make beaker tests honour puppet_gem_version

This commit was correct [1] when it added the
puppet_gem_version ansible var to the jobs to
restrict the gems version in puppet-openstack_spec_helper.

However since we haven't modified it to read the
variable and set the PUPPET_GEM_VERSION environment
variable it wasn't honoured by the spec helper when
it installed the puppet gem like done in [2].

[1] https://review.openstack.org/#/c/632962/
[2] d61f652b0a/playbooks/run-unit-tests.yaml (L6)

Change-Id: I61cb86b42d2ce12e9eabed3aac7b4b185ca987b5

playbooks/run-beaker-tests.yaml

@@ -25,6 +25,9 @@
       shell:
         cmd: |
           trap "{{ ansible_user_dir }}/workspace/openstack/puppet-openstack-integration/copy_logs.sh" EXIT
+          if [ "{{ puppet_gem_version }}" != "latest" ]; then
+            export PUPPET_GEM_VERSION='~> {{ puppet_gem_version }}'
+          fi
           export BEAKER_PUPPET_COLLECTION=puppet5
           export BEAKER_set=nodepool-{{ nodepool_type }}
           export BEAKER_debug=yes

playbooks/run-libraries-beaker-tests.yaml

@@ -25,6 +25,9 @@
           set -e
           set -x
           trap "{{ ansible_user_dir }}/workspace/openstack/puppet-openstack-integration/copy_logs.sh" EXIT
+          if [ "{{ puppet_gem_version }}" != "latest" ]; then
+            export PUPPET_GEM_VERSION='~> {{ puppet_gem_version }}'
+          fi
           export BEAKER_PUPPET_COLLECTION=puppet5
           export BEAKER_set=nodepool-{{ nodepool_type }}
           ./run_beaker_tests.sh

zuul.d/base.yaml

@@ -184,3 +184,4 @@
     voting: false
     vars:
       nodepool_type: bionic
+      puppet_gem_version: latest

zuul.d/beaker.yaml

@@ -51,3 +51,4 @@
       - ^.gitignore$
     vars:
       nodepool_type: bionic
+      puppet_gem_version: latest