Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=57155
Allow a web application to be configured that does not have a docBase on the file system. This is primarily intended for use when embedding.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1635222 13f79535-47bb-0310-9956-ffa450edef68