Added missing CLI argument dropped during last commit.

Added missing CLI argument dropped during last commit.

Oops -- when removing the -cell arguments to the bos commands, the
"admin" username argument to "bos adduser" was mistakenly removed as
well.

Reviewed-on: http://gerrit.openafs.org/2940
Reviewed-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit f1a0239fba5855c5fed418f057bd5397d412e907)
Change-Id: Ib28e6f6ce9cced9d44cfccbb02c10289acd818e1
Reviewed-on: http://gerrit.openafs.org/3054