Replaced "kolla_external_fqdn_cacert" and "kolla_internal_fqdn_cacert" with
"kolla_admin_openrc_cacert". OS_CACERT is now set to the value of
"kolla_admin_openrc_cacert" in the generated admin-openrc.sh file.

Change-Id: If195d5402579cee9a14b91f63f5fde84eb84cccf
Partially-Implements: blueprint add-ssl-internal-network
Depends-On: https://review.opendev.org/#/c/731344/

Update the certificate generation task to create a root CA for the
self-signed certificates. The internal and external facing certificates
are then generated using the root CA.

Updated openstack_cacert to use system CA trust store in CI tests
certificate by default.

Change-Id: I6c2adff7d0128146cf086103ff6060b0dcefa37b
Partially-Implements: blueprint add-ssl-internal-network