Before:
tka initialized at head 325557575a59525354484e4a534f494b4c4e56575435583737564b5036584c4d4c335534554255344c344c36484c5a444a323341
After:
tka initialized at head 2UWWZYRSTHNJSOIKLNVWT5X77VKP6XLML3U4UBU4L4L6HLZDJ23A
Printing the AUM hash as hex makes it difficult to compare to other AUM
hashes; stringifying it will make it consistent with other printing.
Updates #cleanup
Change-Id: Ic1e23a9ce6a71a53cff7d2190f9fa06eb838ab89
Signed-off-by: Alex Chan <alexc@tailscale.com>