RFR: JDK-8301050: Detect Xen Virtualization on Linux aarch64

[Matthias Baesken]

With https://bugs.openjdk.org/browse/JDK-8300266 KVM and VMWare virtualization detection has been added; this should be enhanced by Xen detection.
However it seems that for Xen we should look at other file system locations compared to the other virtualizations.
more /sys/hypervisor/type
xen
seems to be available there.

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Commit messages:
 - JDK-8301050

Changes: https://git.openjdk.org/jdk/pull/12217/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12217&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301050
  Stats: 29 lines in 1 file changed: 17 ins; 6 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/12217.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12217/head:pull/12217

PR: https://git.openjdk.org/jdk/pull/12217