x86: vmx: Allow tests to hand-over test-vmcs between CPUs

By exposing launched, test-vmcs can be hand-over between CPUs
by VMCLEAR test-vmcs and resetting launched to false.

Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>