qemu: Add domain support for VCPU halted state
    
    Adding a field to the domain's private vcpu object to hold the halted
    state information.
    Adding two functions in support of the halted state:
    - qemuDomainGetVcpuHalted: retrieve the halted state from a
      private vcpu object
    - qemuDomainRefreshVcpuHalted: obtain the per-vcpu halted states
      via qemu monitor and store the results in the private vcpu objects
    
    Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
    Reviewed-by: Bjoern Walk <bwalk@linux.vnet.ibm.com>
    Reviewed-by: Hao QingFeng <haoqf@linux.vnet.ibm.com>
    Signed-off-by: Boris Fiuczynski <fiuczy@linux.vnet.ibm.com>