python3: port certmonger requests script

This commit fixes requesting certificates via certmonger in Python 3.
This includes dogtag-ipa-ca-renew-agent-submit script and scripts
used during the scripts restarting.

https://pagure.io/freeipa/issue/4985

Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>

ipaserver/install/dogtaginstance.py

@@ -351,7 +351,8 @@ class DogtagInstance(service.Service):
                 cs_cfg,
                 directive,
                 # the cert must be only the base64 string without headers
-                base64.b64encode(cert.public_bytes(x509.Encoding.DER)),
+                (base64.b64encode(cert.public_bytes(x509.Encoding.DER))
+                 .decode('ascii')),
                 quotes=False,
                 separator='=')