dht: fix rename race

Additional check to check if we created the linkto
file before deleting it in the rename cleanup function

Change-Id: I919cd7cb24f948ba4917eb9cf50d5169bb730a67
BUG: 1138387
Signed-off-by: Nithya Balachandran <nbalacha@redhat.com>
Reviewed-on-master: http://review.gluster.org/8338
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/8605
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>