RFR: JDK-8195789: Building of test/langtools/jdk/jshell/VariablesTest.java may fail

[Jan Lahoda]

When pushing the fix for JDK-8191842, I accidentally broke the 
test/langtools/jdk/jshell/VariablesTest.java test, as it now requires 
access to javac internals to compile. The proposed fix is to add the 
proper @modules tag.

Webrev: http://cr.openjdk.java.net/~jlahoda/8195789/webrev.00/
Bug: https://bugs.openjdk.java.net/browse/JDK-8195789

Sorry for any trouble,
      Jan