KVM: nVMX: Reset RFLAGS on VM-exit

Ouch, how could this work so well that far? We need to clear RFLAGS to
the reset value as specified by the SDM. Particularly, IF must be off
after VM-exit!

Reviewed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>