Description of problem:
when creating vol with owner!=root and vol's allocation_size > pool's available_size, libvirt still created that vol even if an error produced.

Version-Release number of selected component (if applicable):
kernel-3.10.0-350.el7.x86_64
qemu-kvm-rhev-2.3.0-31.el7_2.7
libvirt-1.3.1-1.el7

How reproducible:
100%

steps to reproduce:
1. having a dir pool as follow:
# virsh pool-dumpxml test-pool
<pool type='dir'>
  <name>test-pool</name>
  <uuid>849399e0-3f8b-4652-b003-8a421ad50c08</uuid>
  <capacity unit='bytes'>42141450240</capacity>
  <allocation unit='bytes'>31223828480</allocation>
  <available unit='bytes'>10917621760</available>
  <source>
  </source>
  <target>
    <path>/tmp/pool</path>
    <permissions>
      <mode>0755</mode>
      <owner>0</owner>
      <group>0</group>
      <label>unconfined_u:object_r:user_tmp_t:s0</label>
    </permissions>
  </target>
</pool>

# virsh pool-info test-pool
Name:           test-pool
UUID:           849399e0-3f8b-4652-b003-8a421ad50c08
State:          running
Persistent:     no
Autostart:      no
Capacity:       39.25 GiB
Allocation:     29.08 GiB
Available:      10.17 GiB   <=== left space is 10G

2. prepare a vol xml as follow, set the owner&group to 0 (root), and make sure the vol's allocation size is greater that the pool's available size:
# cat 200G_alloc_raw_root.vol
<volume type='file'>
  <name>200G_alloc.img</name>
  <source>
  </source>
<capacity>214748364800</capacity>  
<allocation>214748364800</allocation>  <!-- 200G -->
<target>
    <path>/tmp/pool/200G_alloc.img</path>
    <format type='raw'/>
    <permissions>
      <mode>0600</mode>
      <owner>0</owner>   <!-- root -->
      <group>0</group>
      <label>system_u:object_r:virt_image_t:s0</label>
    </permissions>
  </target>
</volume>


3. create vol with xml 200G_alloc_raw_root.vol
# virsh vol-create test-pool 200G_alloc_raw_root.vol
error: Failed to create vol from 200G_alloc_raw_root.vol
error: cannot allocate 214748364800 bytes in file '/tmp/pool/200G_alloc.img': No space left on device

4. check the vol in the test-pool
# virsh pool-refresh test-pool; virsh vol-list test-pool
Pool test-pool refreshed

 Name                 Path                                    
------------------------------------------------------------------------------
<==== nothing created as expected.

5. prepare anohter xml as follow and set the owner&group to 107(qemu), and make sure the vol's allocation size is greater that the pool's available size:
# cat 200G_alloc_raw_qemu.vol
<volume type='file'>
  <name>200G_alloc.img</name>
  <source>
  </source>
<capacity>214748364800</capacity>  
<allocation>214748364800</allocation>
<target>
    <path>/tmp/pool/200G_alloc.img</path>
    <format type='raw'/>
    <permissions>
      <mode>0600</mode>
      <owner>107</owner>   <!-- qemu -->
      <group>107</group>
      <label>system_u:object_r:virt_image_t:s0</label>
    </permissions>
  </target>
</volume>

6. try to create vol with xml 200G_alloc_raw_qemu.vol
# virsh vol-create test-pool 200G_alloc_raw_qemu.vol
error: Failed to create vol from 200G_alloc_raw_qemu.vol
error: cannot allocate 214748364800 bytes in file '/tmp/pool/200G_alloc.img': No space left on device

7. check the vol-list of test-pool
# virsh pool-refresh test-pool; virsh vol-list test-pool
Pool test-pool refreshed

 Name                 Path                                    
------------------------------------------------------------------------------
 200G_alloc.img       /tmp/pool/200G_alloc.img   <=== even if step 6 failed, img partially created.

# du -h /tmp/pool/200G_alloc.img
11G        /tmp/pool/200G_alloc.img  <=== even if step 6 failed, img partially created.

Actually result:
Step 6 created a img file.

Expected result:
Step 6 should not create img file as step 3 did.

Note:
The only difference of step 3 and step 6 is that the owner/group in the vols' xml files changed. (root vs. qemu)