Description of problem:
=======================
fallocate created data set is crossing storage reserve space limits resulting 100% brick full.

Note: I created files using dd and the storage reserve space limits are respected as expected. 

Version-Release number of selected component (if applicable):
3.12.2-4.el7rhgs.x86_64

How reproducible:
=================
always

Steps to Reproduce:
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1) create a x3 volume and start it.
2) FUSE mount on a client and make a note of df -h output.
3) Set storage.reserve volume set option to 50,
gluster volume set distrepx3 storage.reserve 50
4) Using fallocate create data on the mount point,
for i in {1..10000};do fallocate -l 1G test_file$i.img;done

Actual results:
===============
fallocate created data set is crossing storage reserve space limits resulting 100% brick full.