RFR: 8227574: Fix jtreg access denied failure with graal mode.

[Xiaohong Gong (Arm Technology China)]

Hi,

Please help to review the following patch that fixes two jtreg tests failure with graal mode due to the access denied issue.
Webrev: http://cr.openjdk.java.net/~pli/rfr/8227574/webrev.00/
JBS: https://bugs.openjdk.java.net/browse/JDK-8227574

JTReg tests:
  jdk/java/net/URLPermission/URLTest.java
  jdk/javax/sql/testng/test/rowset/spi/SyncFactoryPermissionsTests.java
fail due to losing permission of the JVMCI runtime.
This patch fixes the two tests by making their policy extending the default system policy which grants the permissions to jdk.internal.vm.compiler module and its dependencies.

Thanks,
Xiaohong Gong