Application may have a "more secure" data store than the metadata cache
is: Allow application to bootstrap the Updater with this more secure
root. This means the Updater must also cache the subsequent root versions
(and not just the last one).
* Store versioned root metadata in local cache
* maintain a non versioned symlink to last known good root
* When loading root metadata, look in local cache too
* Add a 'bootstrap' argument to Updater: this allows
initializing the Updater with known good root metadata
instead of trusting the root.json in cache
Additional changes to current functionality:
* when using bootstrap argument, the initial root is written to cache.
This write happens every time Updater is initialized with bootstrap
* The "root.json" symlink is recreated at the end of every refresh()
Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>
Instead of having duplicate metadata in examples/ and tests/repository_data, retain only the metadata in tests/repository_data and link to them from METADATA.md
