JENKINS-21377 adapt to tycho-compiler-jdt 0.19.0

This shall fix https://issues.jenkins-ci.org/browse/JENKINS-21377.
Adapted the parser regexp to work with both "[line, column]" and "[line]" as location specs in the Java warning. The latter will be generated by org.eclipse.tycho:tycho-compiler-jdt:0.19.0.