Always pass the plan name to fernet workbook

It was using the default (overcloud) which is not necessarily the case
for every deployment.

This commit passes the TRIPLEO_PLAN_NAME environment file and derives
the value from the passed container name.

Change-Id: I2fc481336b945c88f8b6a017690773be3293a2b4
Closes-Bug: #1742655

workbooks/fernet-key-rotate.yaml

@@ -57,7 +57,7 @@ workflows:
           hosts: keystone
           inventory: /usr/bin/tripleo-ansible-inventory
           ssh_private_key: <% task(get_privkey).result %>
-          extra_env_variables: <% $.ansible_extra_env_variables %>
+          extra_env_variables: <% $.ansible_extra_env_variables + dict(TRIPLEO_PLAN_NAME=>$.container) %>
           verbosity: 0
           remote_user: heat-admin
           become: true