x86: Add test coverage for nested_vmx_reflect_vmexit() testing

Add a framework and test cases to ensure exceptions that occur in L2 are
forwarded to the correct place by nested_vmx_reflect_vmexit().

Add testing for exceptions: #GP, #UD, #DE, #DB, #BP, and #AC.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Message-Id: <20220125203127.1161838-5-aaronlewis@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>