Follow-on to r1617445
If a client certificate is required and one is not available then force renegotiation to obtain it.
If a client certificate is optional then do not force renegotiation before trying to obtain it.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1617461 13f79535-47bb-0310-9956-ffa450edef68