In order to be compliant with how network policies are supposed to work
in K8s, we need to allow all ingress and egress traffic for pods without
any NP applied. This patch ensures such behavior in DevStack by making
it create an allow-all SG and adding it to pod_security_groups when
network policy support is enabled.
Change-Id: I76c9082c52c17c833a22751f4352d0c469f573bd
Closes-Bug: 1822170