Changes to support Kafka over SSL in APEX

Changes to support Kafka over SSL in APEX

The Kafka plugin in APEX-PDP already has a field "kafkaProperties" that
can take in any properties required for the Kafka client. This is apt to
store the SSL related properties as they could change based on the
server implementation.

To make the communication possible, the only change required in APEX is
to allow a property to have an empty value.
For e.g., to disable the server host name verification, ssl.endpoint.identification.algorithm must to be explicitly set to an empty string on the client.

Change-Id: If3adaeaf11e5fbbd2aff582b5d4ba7824017ea8a
Issue-ID: POLICY-3194
Signed-off-by: a.sreekumar <ajith.sreekumar@bell.ca>