Don't reference argparse._StoreAction
Don't reference argparse._StoreAction

This is a private implementation detail of argparse, so we don't want
to rely on it. Just sub-class Action instead.

Change-Id: Icfcc782cc334d1bc1d4940bec23af48ead692a9d

JioCloud/oslo-incubator,JioCloud/oslo-incubator,JioCloud/oslo-incubator