Fix Comet unit test failures on OSX. OSX requires timeout of 0 for non-blocking read

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1521440 13f79535-47bb-0310-9956-ffa450edef68
Reduce timing sensitivity of test as some false positives have been observed.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1521444 13f79535-47bb-0310-9956-ffa450edef68