Add more thorough tests for AJP.

Unfortunately request attributes as sent
by mod_jk JkEnvVars can not be tested,
because request.getAttributeNames() does
not return the names of Coyote request
attributes. Only getAttribute(String)
checks Coyote request attributes.


git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1645488 13f79535-47bb-0310-9956-ffa450edef68