kvm: nVMX: Handle deferred early VMLAUNCH/VMRESUME failure properly

When emulating a nested VM-entry from L1 to L2, several control field
validation checks are deferred to the hardware. Should one of these
validation checks fail, vcpu_vmx_run will set the vmx->fail flag. When
this happens, the L2 guest state is not loaded (even in part), and
execution should continue in L1 with the next instruction after the
VMLAUNCH/VMRESUME.

The VMCS12 is not modified (except for the VM-instruction error
field), the VMCS12 MSR save/load lists are not processed, and the CPU
state is not loaded from the VMCS12 host area. Moreover, the vmcs02
exit reason is stale, so it should not be consulted for any reason.

Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>