Auto merge of #20782 - servo:jdm-patch-13, r=glennw
Auto merge of #20782 - servo:jdm-patch-13, r=glennw

Don't suppress errors when executing mach bootstrap processes.

[Omitting an argument](https://docs.python.org/2/library/sys.html#sys.exit) to sys.exit causes it to default to 0, so buildbot doesn't report it as an error.

We were just lucky that the android builders happened to have a build step that failed that didn't rely on running python!

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szeged/servo,saneyuki/servo,KiChjang/servo,KiChjang/servo,dati91/servo,KiChjang/servo,saneyuki/servo,szeged/servo,DominoTree/servo,jimberlage/servo,emilio/servo,sadmansk/servo,larsbergstrom/servo,DominoTree/servo,nnethercote/servo,notriddle/servo,saneyuki/servo,nnethercote/servo,saneyuki/servo,szeged/servo,ConnorGBrewster/servo,KiChjang/servo,splav/servo,pyfisch/servo,ConnorGBrewster/servo,DominoTree/servo,paulrouget/servo,peterjoel/servo,pyfisch/servo,paulrouget/servo,SimonSapin/servo,paulrouget/servo,SimonSapin/servo,emilio/servo,dati91/servo,paulrouget/servo,notriddle/servo,jimberlage/servo,DominoTree/servo,mbrubeck/servo,SimonSapin/servo,pyfisch/servo,larsbergstrom/servo,larsbergstrom/servo,peterjoel/servo,ConnorGBrewster/servo,pyfisch/servo,nnethercote/servo,peterjoel/servo,szeged/servo,larsbergstrom/servo,sadmansk/servo,nnethercote/servo,nnethercote/servo,cbrewster/servo,nnethercote/servo,SimonSapin/servo,SimonSapin/servo,DominoTree/servo,mbrubeck/servo,szeged/servo,pyfisch/servo,emilio/servo,dati91/servo,KiChjang/servo,sadmansk/servo,peterjoel/servo,saneyuki/servo,emilio/servo,szeged/servo,mbrubeck/servo,jimberlage/servo,dati91/servo,notriddle/servo,jimberlage/servo,paulrouget/servo,nnethercote/servo,emilio/servo,emilio/servo,mbrubeck/servo,paulrouget/servo,paulrouget/servo,szeged/servo,szeged/servo,larsbergstrom/servo,KiChjang/servo,DominoTree/servo,DominoTree/servo,notriddle/servo,splav/servo,sadmansk/servo,saneyuki/servo,KiChjang/servo,nnethercote/servo,peterjoel/servo,emilio/servo,splav/servo,larsbergstrom/servo,pyfisch/servo,saneyuki/servo,ConnorGBrewster/servo,DominoTree/servo,cbrewster/servo,paulrouget/servo,emilio/servo,mbrubeck/servo,notriddle/servo,splav/servo,ConnorGBrewster/servo,nnethercote/servo,jimberlage/servo,saneyuki/servo,notriddle/servo,peterjoel/servo,cbrewster/servo,ConnorGBrewster/servo,dati91/servo,peterjoel/servo,pyfisch/servo,splav/servo,pyfisch/servo,mbrubeck/servo,sadmansk/servo,larsbergstrom/servo,emilio/servo,notriddle/servo,mbrubeck/servo,peterjoel/servo,ConnorGBrewster/servo,paulrouget/servo,notriddle/servo,ConnorGBrewster/servo,SimonSapin/servo,jimberlage/servo,notriddle/servo,peterjoel/servo,nnethercote/servo,larsbergstrom/servo,cbrewster/servo,DominoTree/servo,SimonSapin/servo,dati91/servo,pyfisch/servo,splav/servo,saneyuki/servo,dati91/servo,szeged/servo,paulrouget/servo,splav/servo,cbrewster/servo,saneyuki/servo,KiChjang/servo,peterjoel/servo,KiChjang/servo,larsbergstrom/servo,DominoTree/servo,larsbergstrom/servo,splav/servo,dati91/servo,pyfisch/servo,sadmansk/servo,szeged/servo,cbrewster/servo,KiChjang/servo,jimberlage/servo,cbrewster/servo,sadmansk/servo,emilio/servo,notriddle/servo,splav/servo,jimberlage/servo,jimberlage/servo,sadmansk/servo,cbrewster/servo,mbrubeck/servo,SimonSapin/servo,splav/servo