features/quota: fixes to dentry management code in rename.

1. After a successful rename (src, dst), the dentry
 <dst-parent, dst-basename> would be associated with src-inode.

2. Its src inode that survives if both of src and dst are present.

The fixes are done based on the above two observation.

Change-Id: I7492a512e3732b1455c243b02fae12d489532bfb
BUG: 1140084
Signed-off-by: Raghavendra G <rgowdapp@redhat.com>
Reviewed-on: http://review.gluster.org/8687
Reviewed-by: susant palai <spalai@redhat.com>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>