RFR(XS) 8233888: jdk.vm.ci.hotspot.test.VirtualObjectLayoutTest.testFormat(): Unexpected error verifying

[Tom Rodriguez]

http://cr.openjdk.java.net/~never/8233888/webrev
https://bugs.openjdk.java.net/browse/JDK-8233888

A recently added unit test was making assumptions about field alignment 
that didn't hold when compressed oops were disabled.  The fix is to 
adjust the starting point for the debug info depending on the alignment 
of the first field.  Tested locally with and without compressed oops.

tom