virsh.cpu_baseline: Using baseline cpu to config guest

Signed-off-by: Yanbing Du <ydu@redhat.com>
should move line 102 and 103 into line 74, otherwise, any line 102 or 103 is failed, the codes will jump into 'finally' section then 'vm' is empty, or a safe method is like so:

if vm and vm.alive()
    vm.destroy()