x86: nVMX: add new test for vmread/vmwrite flags preservation

This commit adds new unit tests for commit a4d956b93904 ("KVM: nVMX:
vmread should not set rflags to specify success in case of #PF")

The two new tests force a vmread and a vmwrite on an unmapped
address to cause a #PF and verify that the low byte of %rflags is
preserved and that %rip is not advanced.  The commit fixed a
bug in vmread, but we include a test for vmwrite as well for
completeness.

Before the aforementioned commit, the ALU flags would be incorrectly
cleared and %rip would be advanced (for vmread).

Signed-off-by: Simon Smith <brigidsmith@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Message-Id: <20200420175834.258122-1-brigidsmith@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>