Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=50677

Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=50677
Allow ANT style variables in the common.loader and other *.loader properties in conf/catalina.properties

I do not implement the substitution for any property as suggested by BZ 50677,
but only for the class loader ones. I think this is sufficient for the use case
and does not break backwards compatibility.
Most of the code is copied from ClassLoaderLogManager.replace().

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1136043 13f79535-47bb-0310-9956-ffa450edef68