cloud-init doesn't cache network_config property in cache

This bug was originally filed in Launchpad as [LP: #1716773](https://bugs.launchpad.net/cloud-init/+bug/1716773)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2017-09-12T21:08:38.045018+00:00

date_fix_committed = None

date_fix_released = None

id = 1716773

importance = medium

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1716773

milestone = None

owner = raharper

owner_name = Ryan Harper

private = False

status = confirmed

submitter = raharper

submitter_name = Ryan Harper

tags = []

duplicates = []

_Launchpad user **Ryan Harper(raharper)** wrote on 2017-09-12T21:08:38.045018+00:00_

When init net stage runs, it will restore the cloud object cache in /var/lib/cloud/instance/obj.pkl

This cache dump is created before cloud-init processes the datasource, which means some of the data cloud-init has fetched is not cached.

In particular, we've observed that the 'network_config' attribute is populated and set in init-local mode, but when we run init-net; it will re-run due to the underlying object value still be set to None (the default) as we failed to cache the object after modifying it.

Start by tracing the init-local and init-net stages around the cloud object cache at /var/lib/cloud/instance/obj.pkl, focusing on when network_config is populated and restored. Done means the value set during init-local is persisted and available in init-net without being re-fetched unnecessarily; add or update tests covering that cache flow.

Written by the indexing model from the issue text.