cleaning up diego client

Signed-off-by: Ted Young <tyoung@pivotallabs.com>
renamed update_staging_complete to update_start_command

Signed-off-by: Ted Young <tyoung@pivotallabs.com>
staging on diego is triggered if an app has no detected start command

Signed-off-by: Ted Young <tyoung@pivotallabs.com>
removed unused react_to_package_state_change method from AppObserver

Signed-off-by: Ted Young <tyoung@pivotallabs.com>
when increasing/decreasing instances for a diego app, take the diego route
can now stop apps running on diego