-img: add support for offline rate limit in qemu-img commit
=== TEST SCRIPT BEGIN ===
#!/bin/bash
git rev-parse base > /dev/null || exit 0
git config --local diff.renamelimit 0
git config --local diff.renames True
git config --local diff.algorithm histogram
./scripts/checkpatch.pl --mailback b
From: Zhengui
Currently, there is no rate limit for qemu-img commit. This may
cause the task of qemu-img commit to consume all the bandwidth
of the storage. This will affect the IO performance of other processes
and virtual machines under shared storage. So we add support for
offline rate limit
