Test VM-entry in MOVSS shadow

VM-entry is disallowed in the shadow of a MOV-to-SS instruction. When
the current-VMCS is valid, check that the instruction pointer falls
through to the next instruction, the ALU flags are set to ZF
(VMfailValid), and the VM-instruction error field contains 26 ("VM
entry with events blocked by MOV SS.").

Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>