fixed by making the classloader used by checkForkedPath behave like a real forked classpath, thus completely isolated from the launching jvm

the File constructor seems to be unable to parse URLs created from
URIs sometimes, leading to a test failure. Most likely the spaces or
parentheses inside of the path of the jenkins workspaces are
responsible.

https://bz.apache.org/bugzilla/show_bug.cgi?id=62194