metrics: network: Fix dirty environment
metrics: network: Fix dirty environment

This script fails due to a container is already using
the same name. This happens because it does not clean
the environment before to run the tool/test. This commit
uses a common function in order to clean up the current
containers running.

Fixes: #525

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

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