cacheout: Improve error handling

cacheout: Improve error handling

Bail out when we encounter errors in initialization. Among other
things, this prevents a segfault if we can't read the client
configuration.

Change-Id: I8b35163c5c4750eb05539a225069327051a3f148
Reviewed-on: http://gerrit.openafs.org/2665
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Hutzelman <jhutz@cmu.edu>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>