virttest.qemu_vm : Get vcpu threads by funtion get_vcpu_pids

Now we can using funtion get_vcpu_pids() to get vcpu thread

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>
Shared/cfg/base.cfg: make 'vcpu_thread_pattern' support both type monitors

This patch modify the pattern of 'vcpu_thread_pattern',
make the pattern can support both human and qmp monitor.

Signed-off-by: Yunping Zheng <yunzheng@redhat.com>