Fix stdout spew
Fix stdout spew

Summary: All error messages MUST go to stderr, or they may mess up our json
output.

Reviewed By: @mroch

Differential Revision: D2527073

fb-gh-sync-id: 3851deeb715b1f2e6f9c069638635c33f79e61dd

popham/flow,jeffmo/flow,gabro/flow,samwgoldman/flow,claudiopro/flow,jgrund/flow,samwgoldman/flow,TiddoLangerak/flow,chenglou/flow,jamesgpearce/flow,ForbesLindesay/flow,jeffmo/flow,d14b3l/flow,Eyyub/flow,cesarandreu/flow,jamesgpearce/flow,d14b3l/flow,popham/flow,popham/flow,AgentME/flow,d14b3l/flow,graue/flow,facebook/flow,jdelStrother/flow,TiddoLangerak/flow,nmote/flow,TiddoLangerak/flow,AgentME/flow,gabro/flow,graue/flow,jamesgpearce/flow,jeffmo/flow,popham/flow,facebook/flow,facebook/flow,shiftcars/flow,AprilArcus/flow,jeffmo/flow,mroch/flow,OCamlPro/flow,AgentME/flow,gabelevi/flow,graue/flow,graue/flow,JonathanUsername/flow,ForbesLindesay/flow,OCamlPro/flow,fletcherw/flow,graue/flow,MichaelDeBoey/flow,gabelevi/flow,fletcherw/flow,jamesgpearce/flow,jgrund/flow,ylu1317/flow,gabelevi/flow,jdelStrother/flow,AprilArcus/flow,gabro/flow,cesarandreu/flow,JonathanUsername/flow,nmote/flow,JonathanUsername/flow,ylu1317/flow,JonathanUsername/flow,JonathanUsername/flow,popham/flow,jgrund/flow,facebook/flow,AprilArcus/flow,jamesgpearce/flow,chenglou/flow,chenglou/flow,AgentME/flow,chenglou/flow,cesarandreu/flow,facebook/flow,ForbesLindesay/flow,jdelStrother/flow,samwgoldman/flow,MichaelDeBoey/flow,mroch/flow,fletcherw/flow,claudiopro/flow,popham/flow,mroch/flow,mroch/flow,jgrund/flow,gabelevi/flow,mroch/flow,fletcherw/flow,jeffmo/flow,ylu1317/flow,claudiopro/flow,MichaelDeBoey/flow,jgrund/flow,MichaelDeBoey/flow,nmote/flow,mroch/flow,d14b3l/flow,samwgoldman/flow,claudiopro/flow,TiddoLangerak/flow,gabelevi/flow,ylu1317/flow,graue/flow,TiddoLangerak/flow,cesarandreu/flow,shiftcars/flow,AprilArcus/flow,jdelStrother/flow,fletcherw/flow,Eyyub/flow,Eyyub/flow,facebook/flow,OCamlPro/flow,ForbesLindesay/flow,gabro/flow,jamesgpearce/flow,nmote/flow,Eyyub/flow,AprilArcus/flow,shiftcars/flow,JonathanUsername/flow,OCamlPro/flow,chenglou/flow,gabelevi/flow,ForbesLindesay/flow,mroch/flow,popham/flow,ForbesLindesay/flow,d14b3l/flow,samwgoldman/flow,MichaelDeBoey/flow,nmote/flow,jgrund/flow,AprilArcus/flow,nmote/flow,ylu1317/flow,claudiopro/flow,nmote/flow,AgentME/flow,JonathanUsername/flow,jeffmo/flow,jdelStrother/flow,gabro/flow,samwgoldman/flow,shiftcars/flow,fletcherw/flow,gabro/flow,d14b3l/flow,jamesgpearce/flow,shiftcars/flow,chenglou/flow,shiftcars/flow,samwgoldman/flow,facebook/flow,gabelevi/flow,jdelStrother/flow