buildroot

package/python-configshell-fb: update URL to the open-iscsi organization

Also add a comment to indicate that python-rtslib-fb and targetcli-fb
should be bumped every time python-configshell-fb is bumped because
upstream usually upgrades all of these packages at the same time.

Signed-off-by: Christophe Vu-Brugier <cvubrugier@fastmail.fm>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>