Add :z to volume mount to fix the selinux context.

After merge of [1], In Downstream cockpit, triggering ruck_rover.py
commands from inside telegraf_py3 container are failing with below
error because of selinux issues.

~~~
[root@telegraf_py3 /]# ./usr/local/bin/ruck_rover.py --release osp16-2 --distro rhel-8 --component ui --influx
.
.
OSError: Could not find a suitable TLS CA certificate bundle, invalid path: /etc/pki/ca-trust/extracted/openssl/ca-bundle.trust.crt

[root@telegraf_py3 pki]# ls
ls: cannot open directory '.': Permission denied
~~~

We are not hitting above issue if we set selinux to
permissive mode(setenforce 0) on host.

As per[2], adding z to mount will automatically set the correct selinux
context on host directory, docker will do this automatically
"chcon -Rt svirt_sandbox_file_t /etc/pki".

[1] https://review.rdoproject.org/r/c/rdo-infra/ci-config/+/39335
[2] https://web.archive.org/web/20190728100417/https://www.projectatomic.io/blog/2015/06/using-volumes-with-docker-can-cause-problems-with-selinux/

Change-Id: Ib7a1dd246a7e23aa00b72e911beb87d3b096c137

ci-scripts/infra-setup/roles/rrcockpit/files/docker-compose.yml

@@ -84,7 +84,7 @@ services:
       - influxdb
     volumes:
       - telegraf-volume:/tmp/telegraf_py3
-      - /etc/pki/:/etc/pki/
+      - /etc/pki/:/etc/pki/:z
 
   compare_rpms:
     build: compare_rpms