Description of problem:
For NFS pool creation, to set the owner with '107:107' in pool XML desc, that will lead to pool-build command failed. If the owner set with other user, that also get failed. 

Version-Release number of selected component (if applicable):
libvirt-0.9.4-4.el6.x86_64

How reproducible:
Always

Steps to Reproduce:
# ll /var/lib/libvirt/images/
total 18082424
-rw-------. 1 qemu qemu  2228092928 Dec 29 23:02 foo.img
-rw-------. 1 root root      262144 Dec 29 19:09 foo-new.img
-rw-------. 1 root root  6442450944 Dec 23 00:07 rhel6.img
-rw-------. 1 qemu qemu  6442450944 Jan  3 15:55 test.img
-rw-------. 1 root root 12884901888 Jan  1 20:54 win7.img

# virsh pool-dumpxml netfs-pool
<pool type='netfs'>
  <name>netfs-pool</name>
  <uuid>8db59195-7779-4ef1-313a-ef64c466edf6</uuid>
  <capacity>0</capacity>
  <allocation>0</allocation>
  <available>0</available>
  <source>
    <host name='10.66.4.232'/>
    <dir path='/export'/>
    <format type='nfs'/>
  </source>
  <target>
    <path>/var/lib/libvirt/images/netfs-pool</path>
    <permissions>
      <mode>0755</mode>
      <owner>107</owner>
      <group>107</group>
    </permissions>
  </target>
</pool>

# virsh pool-build netfs-pool
error: Failed to build pool netfs-pool
error: cannot create path '/var/lib/libvirt/images/netfs-pool': Unknown error 18446744073709551615
  
Actual results:
Fail to build nfs pool with owned by qemu.

Expected results:
NFS pool should be built successfully.

Additional info:
Manually create the directory will workaround this issue.

# mkdir /var/lib/libvirt/images/netfs-pool

# virsh pool-build netfs-pool
Pool netfs-pool built