virsh: Fix completion logic to guestvcpus command

virsh: Fix completion logic to guestvcpus command

In case of non-continuous vCPU topology, We can't infer the bitmap size
from the combination of onlineVcpuStr and nvcpus.
We should use virBitmapParseUnlimited here instead of virBitmapParse due
to the bitmap size is unknown.

e.g.:

  <vcpus>
    <vcpu id='0' enabled='yes' hotpluggable='no' order='1'/>
    <vcpu id='1' enabled='yes' hotpluggable='yes' order='2'/>
    <vcpu id='2' enabled='yes' hotpluggable='yes' order='3'/>
    <vcpu id='3' enabled='yes' hotpluggable='yes' order='4'/>
    <vcpu id='4' enabled='yes' hotpluggable='yes' order='5'/>
    <vcpu id='5' enabled='yes' hotpluggable='yes' order='6'/>
    <vcpu id='6' enabled='no' hotpluggable='yes'/>
    <vcpu id='7' enabled='no' hotpluggable='yes'/>
  </vcpus>

 # virsh guestvcpus --domain VM
vcpus          : 0-5
online         : 0-5
offlinable     : 1-5

 # virsh setvcpu --domain VM --disable --vcpulist 2

 # virsh guestvcpus --domain VM --disable --cpulist 4,5

 # virsh guestvcpus --domain VM
vcpus          : 0-1,3-5
online         : 0-1,3
offlinable     : 1,3-5

Before:
 # virsh guestvcpus --domain VM --enable --cpulist <TAB><TAB>
2  4

After:
 # virsh guestvcpus --domain VM --enable --cpulist <TAB><TAB>
4  5

Signed-off-by: Lin Ma <lma@suse.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>