Fix in testLeakFd to avoid potential races during the check

To avoid corrupted tests that leaves fds open, clean the fds before
checking the first fds state.

Change-Id: Ic6a6e0586c3e225771701cd594f485aae9b00b6e
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/24739
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>