Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=57216
Improve handling of invalid context paths.
This adds handling of paths that end with '/', including "/".
This corrects handling of null path. It will now produce "" instead of "/null".

Merged r1640089 r1640276 r1640349 from tomcat/tc8.0.x/trunk.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1640351 13f79535-47bb-0310-9956-ffa450edef68
Correct tests to use the correct context path for ROOT webapp.
Those were printing the warning
"StandardContext.setPath A context path must either be an empty string or start with a '/'"...

Merged r1640363, r1640366 from tomcat/tc8.0.x/trunk.


git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1640367 13f79535-47bb-0310-9956-ffa450edef68