Remove ineffective assignment in subcommand
Remove ineffective assignment in subcommand

No need to assign return value to $rc in subcommand,
value in subcommand can not pass to parent process, plus,
it is never used.

Change-Id: I5f478813c7472d3709e09ff88f2165d5f1cd9097
Signed-off-by: Zhao Lei <aacdd228f50c574b28b524b23f12fb9d52d6e0e3@cn.fujitsu.com>

openstack/training-guides,openstack/training-guides