virsh: Report an error when cpulist parsing fails

virsh: Report an error when cpulist parsing fails

When parsing a cpulist, the virBitmapParse is used. On an invalid
bitmap an error is reported, but the error gets cleared
immediately by subsequent public APIs call, e.g. virDomainFree().
Moreover, we don't check whether bitmap fits into maximal CPU ID
on the host. Therefore the following examples failed without any
error:

 # virsh vcpupin test3 1 aaa

 # virsh vcpupin test3 1 1000

Signed-off-by: Luyao Huang <lhuang@redhat.com>