[TUF autoupdater] Use new autoupdate code for internal testing

[RebeccaMahany]

Relates to #954.

This is the next step toward using our new TUF infrastructure: trigger a reload/restart after a successful update; launcher init performs version selection using the new update library.

Future work + linked PRs

Subsequent PRs will tackle the following (order is not set in stone):

1. Other improvements/refactors (ship a more up-to-date TUF repo, consolidate TUF-heavy work into a separate client for ease of readability)
2. An "update now" functionality tied to control server
3. Eventually removing the old notary autoupdater

Previous work:

1. Run new TUF autoupdater side-by-side with notary autoupdater #1081
2. Expose data and metrics about new TUF autoupdater #1103
3. Point to production TUF infra #1108
4. Perform retry on TUF update #1110
5. Add library manager to handle TUF downloads #1111
6. Small autoupdate improvements #1119
7. Pass knapsack in to tuf autoupdater to simplify configuration #1168
8. [TUF autoupdater] Remove osquery client dependency #1178
9. Move TUF test setup to new package #1188
10. [TUF autoupdater] Check out latest #1185
11. [TUF autoupdater] Include arch in release file path and download file path #1195

[RebeccaMahany]

Superseded by #1268