This change adds an idle state to driver providers which is used to
indicate that the provider should stop performing actions that are not
safe to perform while we bootstrap a second newer version of the
provider to handle a config update.
This is particularly interesting for the static driver because it is
managing all of its state internally to nodepool and not relying on
external cloud systems to track resources. This means it is important
for the static provider to not have an old provider object update
zookeeper at the same time as a new provider object. This was previously
possible and created situtations where the resources in zookeeper did
not reflect our local config.
Since all other drivers rely on external state the primary update here
is to the static driver. We simply stop performing config
synchronization if the idle flag is set on a static provider. This will
allow the new provider to take over reflecting the new config
consistently.
Note, we don't take other approaches and essentially create a system
specific to the static driver because we're trying to avoid modifying
the nodepool runtime significantly to fix a problem that is specific to
the static driver.
Change-Id: I93519d0c6f4ddf8a417d837f6ae12a30a55870bb
2a231a08c9