Description of problem:
When using the cpu_realtime and cpu_realtim_mask flag to create new instance, the 'cpuset' of 'emulatorpin' option is using the id of vcpu which is incorrect. The id of host cpu should be used here.

e.g.
  <cputune>
    <vcpupin vcpu='0' cpuset='2'/>
    <vcpupin vcpu='1' cpuset='3'/>
    <emulatorpin cpuset='0'/>          ### the cpuset should be '2' here, when cpu_realtime_mask=^0.  
    <vcpusched vcpus='1' scheduler='fifo' priority='1'/>
  </cputune>

Version-Release number of selected component (if applicable):
1:12.0.2-5.el7ost

How reproducible:
Boot new instance with cpu_realtime_mask flavor.

Steps to Reproduce:
1. Create RT flavor
nova flavor-create m1.small.performance 6 2048 20 2
nova flavor-key m1.small.performance set hw:cpu_realtime=yes
nova flavor-key m1.small.performance set hw:cpu_realtime_mask=^0
nova flavor-key m1.small.performance set hw:cpu_policy=dedicated
2. Boot a instance with this flavor
3. Check the xml of the new instance

Actual results:
  <cputune>
    <vcpupin vcpu='0' cpuset='2'/>
    <vcpupin vcpu='1' cpuset='3'/>
    <emulatorpin cpuset='0'/>          
    <vcpusched vcpus='1' scheduler='fifo' priority='1'/>
  </cputune>

Expected results:
  <cputune>
    <vcpupin vcpu='0' cpuset='2'/>
    <vcpupin vcpu='1' cpuset='3'/>
    <emulatorpin cpuset='2'/>          
    <vcpusched vcpus='1' scheduler='fifo' priority='1'/>
  </cputune>

Additional info: