bozo: cap retry delay

Cap the retry delay to a reasonable amount of time instead
of just doubling the delay until it reaches 16 hours.

Change-Id: Ibc7dd75670a9b02f34050842b6e54df4f5a7c315
Reviewed-on: http://gerrit.openafs.org/10148
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>