serverutil/signup: add info log messages for requests/confirmations
serverutil/signup: add info log messages for requests/confirmations

Also tidy up the existing log messages.

Change-Id: I32a886c64f77dcf36f50a9b6532ffc7b63c2cbdb
Reviewed-on: https://upspin-review.googlesource.com/16180
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/upspin,upspin/upspin