This allows access to external networks to be controlled via the
RBAC framework added during Liberty with a new 'access_as_external'
action.
A migration adds all current external networks to the RBAC policies
table with a wildcard indicating that all tenants can access the network
as RBAC.
Unlike the conversion of shared networks to RBAC, the external table
is left in the DB to avoid invasive changes throughout the codebase
to calculate the flag relative to the caller. So the current 'external'
flag is used throughout the code base as it previously was for wiring
up floating IPs, router gateway ports, etc. Then the RBAC entries are
only referenced when determining what networks to show the tenants.
API Behavior:
* Marking a network as 'external' will automatically create a wildcard
entry that allows that network to be accessed by all tenants.
* An external network may have all of its RBAC entries deleted and then
only an admin will be able to attach to it.
* An RBAC 'access_as_external' entry cannot be deleted if it is required
for a tenant that currently has a router attached to that network.
* Creating an 'access_as_external' RBAC entry will automatically convert
the network into an external network. (This is to enable a workflow
where a private external network is never visible to everyone.)
* The default policy.json will prevent a non-admin from creating wildcard
'access_as_external' RBAC entries to align with the current default policy
we have on setting the 'external' field on the network to prevent poluting
everyone else's network lists.
* The default policy.json will allow a tenant to create an
'access_as_external' RBAC entry to allow specific tenants
(including itself) the ability to use its network as an external network.
Closes-Bug: #1547985
DocImpact: External networks can now have access restricted to small subsets
of tenants
APIImpact: 'access_as_external' will be allowed as an action in the RBAC
API for networks
Change-Id: I4d8ee78a9763c58884e4fd3d7b40133da659cd61