storage/posix: removing deleting entries in case of creation failures

The code is not atomic enough to not to delete a dentry created by a
prallel dentry creation operation.

Change-Id: I9bd6d2aa9e7a1c0688c0a937b02a4b4f56d7aa2e
BUG: 1138387
Signed-off-by: Raghavendra G <rgowdapp@redhat.com>
Reviewed-on-master: http://review.gluster.org/8327
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Reviewed-on: http://review.gluster.org/8693
Tested-by: Vijay Bellur <vbellur@redhat.com>