x86: basic vmwrite/vmread test

Issues VMWRITE to every VMCS field and the checks that VMREAD returns
the expected result. Some tricky cases: read-only fields (skipped),
not-yet-implemented fields (skipped, VMREAD fails with VMfailValid),
guest segment access rights fields (reserved bits are zeroed by the
CPU, so only check non-reserved bits).

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20170421005004.137260-10-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>