virsh_edit: Resolve random/obscure timing failure

Periodically I was getting a failure when the first of the sequence
of virsh_edit's are run in one my long runs using the "--tests virsh"
option. The failing test is/was 'virsh.edit.normal_test.id_option'.
When run alone using "--tests virsh.edit" - the error didn't occur.
After looking at the test for a while I noticed that part of the
processing is to shutdown the guest prior to the last modify_vcpu()
call. Doing that means the 'id' is no longer valid - thus a failure
could occur that wasn't expected. Even after changing that I got a few
more failures and after an attempt to change the sleep() time from 1 to 2
I was directed to the remote.handle_prompts() call which should work.