Clear blocking due to STI or MOV SS in the hypervisor when an instruction is
emulated or when the vcpu incurs an exception. This matches the CPU behavior.

Remove special case code in HLT processing that was clearing the interrupt
shadow. This is now redundant because the interrupt shadow is always cleared
when the vcpu is resumed after an instruction is emulated.

Reported by: David Reed (david.reed@tidalscale.com)
MFC after: 2 weeks