This allows users to create tags (or properties in the case of OpenStack)
on instances using string interpolation values. The use case is to be
able to add information about the tenant* which requested the instance
to cloud-provider tags.
* Note that ultimately Nodepool may not end up using a given node for
the request which originally prompted its creation, so care should be
taken when using information like this. The documentation notes that.
This feature uses a new configuration attribute on the provider-label
rather than the existing "tags" or "instance-properties" because existing
values may not be safe for use as Python format strings (e.g., an
existing value might be a JSON blob). This could be solved with YAML
tags (like !unsafe) but the most sensible default for that would be to
assume format strings and use a YAML tag to disable formatting, which
doesn't help with our backwards-compatibility problem. Additionally,
Nodepool configuration does not use YAML anchors (yet), so this would
be a significant change that might affect people's use of external tools
on the config file.
Testing this was beyond the ability of the AWS test framework as written,
so some redesign for how we handle patching boto-related methods is
included. The new approach is simpler, more readable, and flexible
in that it can better accomodate future changes.
Change-Id: I5f1befa6e2f2625431523d8d94685f79426b6ae5
6320b06950