Fix localfs functional tests in Fedora 18

localfs storage backend is placed in /tmp, however /tmp is tmpfs in
Fedora 18 and it does not support direct IO, so we can not use it for
storing the backend data and the tests fail.

This patch create localfs storage backend in /var/tmp.

Change-Id: I461d35a3698725a03b8512cff1bf9a36e7a8b9ed
Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/12593
Tested-by: oVirt Jenkins CI Server
Reviewed-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>