WINDUP-190  Change all tests' CWD to target/

Might need to fix some tests which use a hard-coded path to src/main/java or such.
A test was failing, and as always, I was getting 
org.jboss.windup.util.exception.WindupException_$$_javassist_ede3de05-4e34-4577-a2ac-c1ef2a2a1f29: null
I have to resort to println() every time I debug.
Sometimes I leave it there by mistake.