It maybe desirable to not generate stats for ephemeral containers.
This commit adds an env variable EXCLUDE_CONTAINER_NAME which is a regex, if it matches
then the container is excluded from the cpu and memory graphs.
Added parallel processing using python's muliprocessing module
to fork a new process each for each docker container when gathering
stats.
This vastly improves performance since using a for loop the script
blocks until the stats are returned.