[testbug] VectorGatherScatterTest.java fails on SVE with -XX:MaxVectorSize=8 after JDK-8288397

This test case was firstly introduced in JDK-8288397.
It fails on SVE with "-XX:MaxVectorSize=8" specified.

-------------------------------------------------------------------------------------
How to reproduce:
make test TEST="test/hotspot/jtreg/compiler/vectorapi/VectorGatherScatterTest.java" JTREG="VM_OPTIONS=-XX:MaxVectorSize=8 -Djdk.incubator.vector.test.loop-iterations=300"

--------------------------------------------------------------------------------------
Error log:
Error Output
------------
OpenJDK 64-Bit Server VM warning: SVE does not support vector length less than 16 bytes. Disabling SVE.
WARNING: Using incubator modules: jdk.incubator.vector
Exception in thread "main" java.lang.ExceptionInInitializerError
        at java.base/java.lang.Class.forName0(Native Method)
        at java.base/java.lang.Class.forName(Class.java:391)
        at java.base/java.lang.Class.forName(Class.java:382)
        at compiler.lib.ir_framework.test.TestVM.getClassObject(TestVM.java:172)
        at compiler.lib.ir_framework.test.TestVM.main(TestVM.java:160)
Caused by: java.lang.IllegalArgumentException: Bad vector bit-size: 32
        at jdk.incubator.vector/jdk.incubator.vector.VectorShape.forBitSize(VectorShape.java:141)
        at compiler.vectorapi.VectorGatherScatterTest.<clinit>(VectorGatherScatterTest.java:56)
        ... 5 more
  #############################################################
   - To only run the failed tests use -DTest, -DExclude,
     and/or -DScenarios.
   - To also get the standard output of the test VM run with
     -DReportStdout=true or for even more fine-grained logging
     use -DVerbose=true.
  #############################################################
compiler.lib.ir_framework.driver.TestVMException: There were one or multiple errors. Please check stderr for more information.
        at compiler.lib.ir_framework.driver.TestVMProcess.throwTestVMException(TestVMProcess.java:238)
        at compiler.lib.ir_framework.driver.TestVMProcess.checkTestVMExitCode(TestVMProcess.java:219)
        at compiler.lib.ir_framework.driver.TestVMProcess.<init>(TestVMProcess.java:74)
        at compiler.lib.ir_framework.TestFramework.runTestVM(TestFramework.java:729)
        at compiler.lib.ir_framework.TestFramework.start(TestFramework.java:701)
        at compiler.lib.ir_framework.TestFramework.start(TestFramework.java:332)
        at compiler.lib.ir_framework.TestFramework.runWithFlags(TestFramework.java:240)
        at compiler.vectorapi.VectorGatherScatterTest.main(VectorGatherScatterTest.java:145)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
        at java.base/java.lang.reflect.Method.invoke(Method.java:578)
        at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
        at java.base/java.lang.Thread.run(Thread.java:1589)JavaTest Message: Test threw exception: compiler.lib.ir_framework.driver.TestVMException: There were one or multiple errors. Please check stderr for more information.
JavaTest Message: shutting down test