Log some progress info to make updates more debuggable. Also, track
whether an active update is already started and return an error if
a concurrent update is attempted.
Some planned future PRs:
* add JSON output to `tailscale update`
* use JSON output from `tailscale update` to provide a more detailed
status of in-progress update (stage, download progress, etc)
Updates #6907
Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
Andrew Lytvynov
1073b56e18