Storage Throughput metrics are incorrect in Overview

This bug is a backport clone of [Bugzilla Bug 2071491](https://bugzilla.redhat.com/show_bug.cgi?id=2071491). The following is the description of the original bug:
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Description of problem:

Go to Virtualization -> Overview and scroll to the bottom. Watch "Storage Throughput". The statistics seem very wrong.

Version-Release number of selected component (if applicable):
4.10.5

How reproducible:
100%

Steps to Reproduce:
1. Create a VM, do some very little IO (i.e. dd 1G to disk)
2. Virtualization -> Overview
3. Watch Storage Throughput in the statistics at the bottom

Actual results:

• Wrong, impossible values that persist even after the write finished.

Expected results:

• Correct value

Additional info:

• Same is happening for "Node", just select "Node" instead of "VM"