metrics: network: Fix/simplify CPU test
metrics: network: Fix/simplify CPU test

This commit allows to work with runc runtime,
furthermore it removes redundant/deprecated code
and it adds more comments to the code.

Another addition is to enable "exit immediately" if a
pipeline return non-zero status.

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

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