Validate network downtime during live migration

This patch adds the ability to measure network downtime during live
migration process.
A fixture has been added to start and stop a background pinger
process and also read status from it.
The downtime measurement has 0.2 seconds granularity.
In order to reduce overall traffic the ping payload size set to
minimal value.

Change-Id: I83c6a5d49f5d4da05deb677907e5048ecdd2242b
4 files changed