Add tests to verify tomcat functions properly when clustering JARs are not present at runtime

[csutherl]

This change follows up on 91ac751 and a few other recent commits which make cluster classloading fully dynamic by using reflection to handle clustering classes that are missing at runtime. These tests verify that tomcat work correctly when catalina-ha.jar and catalina-tribes.jar are not present using filtering classloaders to simulate that environment.

The tests cover:

• Catalina startup: Tomcat starts and serves requests when clustering classes are unavailable (addClusterRuleSet() logs instead of failing)
• sessionsList.jsp: The Manager app sessions page compiles and renders without clustering, exercising the reflection-based fallback from 91ac751
• StandardEngineSF/StandardHostSF: StoreConfig classes load without error; clusterValveClass fields are null when clustering is absent
• StoreRegistry.getInterfaces(): Returns only the 10 core interfaces (no clustering interfaces) when clustering classes are not on the classpath

Each test uses a custom classloader (NoClusterClassLoader or StoreConfigIsolatingClassLoader) that throws a ClassNotFoundException for org.apache.catalina.ha.* and org.apache.catalina.tribes.* packages.

They're just a tests but I'm submitting this PR for some feedback since it's a bit of a hacky solution before committing.