[transformers] log warn if a transformer exits non-zero
[transformers] log warn if a transformer exits non-zero

keymone/sensu,crewton/sensu,m4ce/sensu,zuazo-forks/sensu,miyakawataku/sensu,Tapjoy/sensu-mirror,quodlibetor/sensu,yonglehou/sensu,somic/sensu,sensu/sensu,javrasya/sensu,solarkennedy/sensu,rbramwell/sensu,upfluence/sensu,npe9/sensu,portertech/sensu,pauloconnor/sensu,withnale/sensu,cread/sensu,bf4/sensu,roobert/sensu