This is part of the transition to using framework/log instead
of the Logf inside the framework package. This will help with
import size/cycles when importing the framework or subpackages.
The e2e iPerf test case currently only runs in IPv4 mode.
This change add an option to run an iPerf test in IPv6 mode (i.e. by running
iPerf with a "-V" command line flag), so that the test can be run on
IPv6-only clusters.
