bosserver: Catch failures to create daemon thread

If we can't create the bozo daemon thread, then don't keep going
regardless. Just warn the user and exit.

Caught by coverity (#988414)

Change-Id: I46445b1744f7c3c944e917b33a6fc6fb669df002
Reviewed-on: http://gerrit.openafs.org/9269
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>