metrics: network: re-factor iperf tests
metrics: network: re-factor iperf tests

This commit removes redundant lines and restrict the
use of "--privileged" flag just when the runtime is
runc.

Fixes: #617

Signed-off-by: Arevalo, Mario Alfredo C <962470f5d16f97233f38b7e7baf23f990a7fbec3@intel.com>

MarioCarrilloA/tests,MarioCarrilloA/tests,chavafg/tests,devimc/tests,clearcontainers/tests,clearcontainers/tests,devimc/tests,chavafg/tests