Comment 1 for bug 1629133

It seems that the tests for network auto allocation need at least four subnets within each subnet pool (v4+v6).

The issue with reusing the FIXED_RANGE* settings as subnet pools is that the former were intended to be used as a single network, while the subnet pools will be split up into multiple subnets. So in particular FIXED_RANGE_V6 is defined as a /64, which is the proper size for a single network, but using that for SUBNETPOOL_PREFIX_V6 would need to chop it into pieces smaller than /64, which will not work with SLAAC.

So my proposal has two parts:

1. Update devstack-gate to set the SUBNETPOOL* variables in a way that the behaviour in the gate will be similar to what was happening before. It will not be identical, since we need to split the /20 into four /22s, but that should resolve the current failures. https://review.openstack.org/379521

2. Update devstack to have more sensible defaults for the subnet pools. Using all of 10/8 seems pretty greedy and should be changed. Using the documentation prefix as a real world default value also seems broken, probably setting SUBNETPOOL_PREFIX_V6 to some random prefix from fd00::/8 like we do for FIXED_RANGE_V6 would be more sensible.