bos: Don't overflow cellname buffer

bos: Don't overflow cellname buffer

Don't overflow the fixed sized cellname buffer when copying the
information in from the command line - instead, just use a
dynamically allocated buffer.

Caught by coverity (#985775)

Change-Id: If87b1ba9bcb990d3145a89627e212144cd78f5a0
Reviewed-on: http://gerrit.openafs.org/9549
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>