RFR(XS) : 8204978: Disable Epsilon GC tests from running with Graal

[Ekaterina Pavlova]

Hello,

Graal does not support Epsilon GC and gc/epsilon tests need to be excluded from execution with Graal.
Please review the fix which adds "@requires !vm.graal.enabled" to disable Epsilon GC tests from running with Graal.

JDK-8184349 is going to address jvm issue to exit gracefully in case GC does not support JVMCI.
Right now Epsilon GC will crash with Graal.

     JBS: https://bugs.openjdk.java.net/browse/JDK-8204978
  webrev: http://cr.openjdk.java.net/~epavlova//8204978/webrev.00/index.html
testing: tested by running GC tests with Graal and checked that all gc/epsilon were excluded.

Thanks,
-katya

p.s.
  Igor Ignatyev volunteered to sponsor this change.