Fix snapshots tests failing bug 1022670
Fix snapshots tests failing
bug 1022670

When running snapshot test, FLAGS.instances_path is defined as '',
with snapshot_directory='/snapshots' which will fail to to permissions errors.

Modified class LibvirtConnTestCase to use libvirt_snapshots_directory=''

Change-Id: I930e4f30ddffcf66c58312e92f0ae368e770e438

n0ano/ganttclient