This adds a new variable for the iptables role that allows us to
indicate all members of an ansible inventory group should have
iptables rules added.
It also removes the unused zuul-executor-opendev group, and some
unused variables related to the snmp rule.
Also, collect the generated iptables rules for debugging.
Change-Id: I48746a6527848a45a4debf62fd833527cc392398
Depends-On: https://review.opendev.org/728952
085856e318