(PUP-672) TrustedInformation handles a nil certificate.

Acceptance caught an issue with an external ca not passing the
certificate info (the
acceptance/tests/external_ca_support/apache_external_root_ca.rb had this
issue prior to +ExportCertData being added to the SSLOptions in
acceptance/tests/external_ca_support/fixtures/httpd.conf).

Modifying the TrustedInformation class to handle a nil certificate
without failure, but issue an info level warning in the logs.

This also modifies the acceptance test to add the +ExportCertData, and
to ensure a teardown, as failure to reach the teardown is breaking
following tests when the httpd server was left up as master.