Don't fail symlinking puppet modules if directory exists

When creating symlinks in /etc/puppet/modules, don't fail if a directory
already exists. This fixes a problem when using puppet module artifacts.

Change-Id: I97d4c127a9f29e99946845660a810e89ea938bee

tripleo_ansible/roles/tripleo_bootstrap/tasks/main.yml

@@ -62,6 +62,10 @@
 - name: Symlink puppet modules under /etc/puppet/modules
   shell: >-
     ln -f -s /usr/share/openstack-puppet/modules/* /etc/puppet/modules/
+  register: result
+  failed_when:
+    - result.rc != 0
+    - "'cannot overwrite directory' not in result.stderr"
   tags:
     - skip_ansible_lint