quick-read: various fixes

- initialize xdata in qr_lookup even if it was NULL from top. This
  allows qr to do its job even if lookup originated from fuse-resolve.c

- extend test cases to include 1 second delay and retry

- fix bug while checking condition for cached unwind

  qr_readv_cached() unwinds if op_ret > 0. Therefore qr_readv()
  must wind to subvol only if !(op_ret > 0) (i.e, op_ret <= 0).

- qr_readv_cached() is using uninitialized @conf pointer. Thanks
  to Raghavendra Bhat for catching this!

Change-Id: Ifaf2ea2685e452210ef9ba3c2d1f2ab51900650c
BUG: 846240
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/4452
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>