webadmin: 'Add Users and Groups' dialog the column size should be limited

The column with the long name looks long
and we need to scroll right/left to see
the other columns

Change-Id: Ia3009bffce854cc99031ad6571affea328c437d1
Bug-Url: https://bugzilla.redhat.com/1126283
Signed-off-by: Ravi Nori <rnori@redhat.com>