Found during JDK-8310110 when the Tracing test would mysteriously fail for the THP case with Shenandoah.

When committing the AUX bitmap (which we do only when needed), we don't hand in the THP page size to os::commit. So Aux bitmap uses system page size.

I'm not sure if this is deliberate or not. It may be deliberate since the AUX bitmap is short-lived, so coalescing the pages may be not what we want. In that case, we should reserve the aux bitmap with system page size. If this is not deliberate, we should call os::commit() with the alignment parameter set to page size to cause it to madvise correctly.