RFR(T/XS): 8236211 [Graal] compiler/graalunit/GraphTest.java is skipped in all testing

[Ekaterina Pavlova]

Hi All,

Please review the small patch which adds required --add-opens required for
org.graalvm.compiler.graph tests (compiler/graalunit/GraphTest.java).
Also removed unnecessary "@requires vm.graal.enabled" from compiler/graalunit/NodesTest.java.
Both tests will start running in graal tiers after this fix
(these tests are now skipped because graalunit tests are tested only in non Graal as JIT mode).

       JBS: https://bugs.openjdk.java.net/browse/JDK-8236211
    webrev: http://cr.openjdk.java.net/~epavlova/8236211/webrev.00/index.html
   testing: graal tiers


thanks,
-katya