Fix passing custom CA cert via DDF params

The verify_credentials method is looking for "ca_certs" in the
default_endpoint hash but the key is "certificate_authority".

This means even if the user passes in a valid CA cert the verify call
will fail because ca_certs will be `nil`

```
server, port, verify_ssl, ca_certs = default_endpoint&.values_at(
  "hostname", "port", "verify_ssl", "ca_certs"
)
(byebug) ca_certs
nil
(byebug) default_endpoint.keys
["hostname", "verify_ssl", "certificate_authority", "port"]
```

app/models/manageiq/providers/ovirt/infra_manager/api_integration.rb

@@ -215,8 +215,8 @@ def verify_credentials(args)
       metrics_authentication = args.dig("authentications", "metrics")
 
       username, password = default_authentication&.values_at("userid", "password")
-      server, port, verify_ssl, ca_certs = default_endpoint&.values_at(
-        "hostname", "port", "verify_ssl", "ca_certs"
+      server, port, verify_ssl, certificate_authority = default_endpoint&.values_at(
+        "hostname", "port", "verify_ssl", "certificate_authority"
       )
 
       metrics_username, metrics_password = metrics_authentication&.values_at("userid", "password")
@@ -230,7 +230,7 @@ def verify_credentials(args)
         :server           => server,
         :port             => port,
         :verify_ssl       => verify_ssl,
-        :ca_certs         => ca_certs,
+        :ca_certs         => certificate_authority,
         :metrics_username => metrics_username,
         :metrics_password => ManageIQ::Password.try_decrypt(metrics_password),
         :metrics_server   => metrics_server,