Improve test for BZ 54928: Cut down wait time by using Thread.join(time) instead of Thread.sleep().

The actual wait time after the change becomes 2s instead of 250ms.
Merged r1634260 from tomcat/trunk.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1634261 13f79535-47bb-0310-9956-ffa450edef68