output stderr for plugin commands
output stderr for plugin commands

[fixes #128457169]

Signed-off-by: Difan Zhao <d4b657a67385123ddb690ebdb0d79b9c6cd38927@pivotal.io>

simonleung8/cli,simonleung8/cli,fujitsu-cf/cli,fujitsu-cf/cli,hyenaspots/cli,markstgodard/cli,hyenaspots/cli,fujitsu-cf/cli,hyenaspots/cli,markstgodard/cli,markstgodard/cli,markstgodard/cli,simonleung8/cli,hyenaspots/cli