Previously we used t.Logf indirectly via package log. This worked, but
it was not ideal for our needs. It could cause the streams of output to
get crossed. This change uses a logger.FuncWriter every place log.Output
was previously used, which will more correctly write log information to
the right test output stream.
Signed-off-by: Christine Dodrill <xe@tailscale.com>
e0f0d10672