tests/func: update output to fix false error

We can't delete a non-empty container now.

Reviewed-by: Robin Dong <sanbai@taobao.com>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>
sheep: small improvement of help message and man page description

We don't have to emphasize that corosync is a default cluster driver
in the help message. In addition, the description can conflict with
the constant DEFAULT_CLUSTER_DRIVER introduced in
6086bf0a3230. Because the value can be "local" if the build
environment doesn't have corosync.

Reported-by: Marcin Miroslaw <marcin@mejor.pl>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>