Fix plugin cache bug when plugin classes are unavailable.

  - If a particular cached plugin's class cannot be loaded, then the 
  entire plugin cache loading would fail! This is undesired, so I've 
  made the plugin cache loading more robust to errors.
  - Rearranged plugin encoding method to help silence static code 
  analyzer complaints about closing resources properly.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1585244 13f79535-47bb-0310-9956-ffa450edef68
Make log less spammy.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1585248 13f79535-47bb-0310-9956-ffa450edef68
Fix problem with nested plugin classes.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1585249 13f79535-47bb-0310-9956-ffa450edef68
Simplify test configs.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1585251 13f79535-47bb-0310-9956-ffa450edef68