Use ui-out table in "maint print reggroups"

This changes the "maint print reggroups" command to use a ui-out table
rather than printf.

It also fixes a typo I noticed in a related test case name; and lets
us finally remove the leading \s from the regexp in completion.exp.

Reviewed-by: Christina Schimpe <christina.schimpe@intel.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>