new: clean up the group name input code

new: clean up the group name input code

Clean up the code that reads group names in from the command line to
take advantage of the read command's ability to display a prompt.  While
we're at it, we should abort the script if the group list encounters
EOF, and we can tighten up some of the other sh-isms too.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>