Clean-up. No functional change.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1551986 13f79535-47bb-0310-9956-ffa450edef68
Refactoring the starting of individual filters into a separate private method so it can be reused elsewhere in the class.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1551991 13f79535-47bb-0310-9956-ffa450edef68