Description of problem:

 when migrating a guest from a host to another ( with a shared storage pool )
 the source guest stay defined on the previous host

Version-Release number of selected component (if applicable):

 i am using 0.8.6  from RHEL6.1  or SL6.1

How reproducible:

 always

Steps to Reproduce:
1.
  with virt-manager, connect to 2 hosts with a common shared storage
2.
  select migrate menu to a new host
3.
  
Actual results:

 the guest is correctly migrated to the new host, but stay defined 
  ( switched off ) on the previous host

Expected results:

 the guest should be undefined on the previous host 
 similarly as if the migration was done with the virsh CLI tool 
 with the migrate --undefinesource option.

Additional info: 

 it is more an enhancement than a bug, but i think the default should be 
 to undefine source , or at least propose an option to behave like this.

 because when you have a lot of guests, it is VERY EASY to miss that a guest
 was already migrated and running to another host, and nothing prevent you
 to switch on this guest again.  ( i have just done it! )

 this is VERY dangerous, because with shared storage, booting a guest twice
 will certainly lead to data corruption.