trunk cannot bootstrap 1.10

[William Reade]

...because we added fields to environments.yaml, that get passed into the 1.10 jujud at bootstrap time, and cause it to fall over.

Thankfully that information -- state-port and api-port -- are actually already present on the bootstrap node, and can be picked up anyway by the code that needs it, without actually requiring a format change.

However, we should also fix 1.10.1, such that it logs and continues when it finds unknown fields in an environment configuration.