fix import-external-cluster.sh in order to work with set -e bash directive, see issue https://github.com/rook/rook/issues/12412
fix documentation mispell in namespace word
Closes: https://github.com/rook/rook/issues/12412
Signed-off-by: mysiki <hoaxboy@wanadoo.fr>
(cherry picked from commit b5d0d80444)