Description
Deactivate memory balloon with type of none get wrong error info

Version
qemu-kvm-rhev-0.12.1.2-2.295.el6.x86_64
kernel-2.6.32-279.el6.x86_64
libvirt-0.9.10-21.el6_3.1.x86_64

How reproducible:
100%

Steps to Reproduce
Setup:
1. Modify the guest xml to deactivate memory balloon, Change memballoon model value as none.

    ...
    <memballoon model='none'>
    </memballoon>
    ...

2. # virsh start test
Domain test started

3. # virsh setmem test 524288
error: Requested operation is not valid: cannot set memory of an active domain
(this error info let we think we can set memory of an inactive domain)

But
4. # virsh destroy test
Domain test destroyed

5. # virsh setmem test 524288
error: Requested operation is not valid: domain is not running

Actual results：
As steps.

Expected results:
Give right error info in cmd line as like:
error: Requested operation is not valid: cannot set memory for memballoon is not active.

Additional info:
when guest running with  <memballoon model='virtio'>, setmem is working well.

# virsh setmem test 524288

# virsh dominfo mig
Id:             25
Name:           test
UUID:           74b67915-0115-fc45-25c2-d6762ed49cdd
OS Type:        hvm
State:          running
CPU(s):         4
CPU time:       22.4s
Max memory:     1048576 kB
Used memory:    524288 kB
Persistent:     yes
Autostart:      disable
Managed save:   no
Security model: selinux
Security DOI:   0
Security label: system_u:system_r:svirt_t:s0:c720,c1022 (enforcing)