Xacml-pdp should not use RestServerParameters for client parameters

The class, XacmlPdpParameterGroup, in the xacml-pdp has a field, policyApiParameters, which is defined as RestServerParameters.  However, that class is for defining parameters used by servers, not clients.  One unfortunate side effect of this is that it precludes the possibility of specifying the use of self-signed certificates during testing.

The field type should be changed to BusTopicParams, which is what other components use to specify parameters for HTTP client connections.  (Or we should create a new common type, RestClientParameters, in policy-common, and change everything to use that instead.)

In addition, the code should be enhanced to allow the use of self-signed certificates, when specified.