Fix test relying on JVM warning being stripped from output

Fix test relying on JVM warning being stripped from output

The line in which warnings like "Archived non-system classes are
disabled because the java.system.class.loader property is specified"
appears can start with e.g."OpenJDK 64-Bit Server VM" or "Java
HotSpot(TM) 64-Bit Server VM". Therefore, an exact match on the former
worked on Linux, but not on Windows, or maybe the difference is
generally between Oracle and OpenJDK. anyway, I use Oracle on Windows
and my build failed. Now it is fixed because I made the match more
generic using a regex.

I also removed a now obsolete check for the occurrence of the stripped
line in test "JDK14 LTW with XML".

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>