Add convenience method to InitialLoggerContext to get a ListAppender (and throw an exception if one isn't found by that name).

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1596450 13f79535-47bb-0310-9956-ffa450edef68
Make clear() return this for easier chaining in tests.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1596452 13f79535-47bb-0310-9956-ffa450edef68
Refactor test to use InitialLoggerContext.

  - Removed * static import on Level.
  - Made Expected a static inner class.
  - Assertion statement clarifications.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1596453 13f79535-47bb-0310-9956-ffa450edef68