VMX: Check unconditional I/O exiting

Test if we ignore "unconditional I/O exiting" as long as "use I/O
bitmap" is enabled. Also test if unconditional exiting itself works.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>