Auto merge of #20024 - servo:jdm-patch-17, r=emilio
Auto merge of #20024 - servo:jdm-patch-17, r=emilio

Propagate error code from fetching WPT changes.

http://build.servo.org/builders/mac-nightly/builds/606 shows a completely error-free run, despite encountering an error early on in `./etc/ci/update-wpt-checkout fetch-and-update-expectations`. We were swallowing the nonzero error code in this case.

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SimonSapin/servo,canaltinova/servo,larsbergstrom/servo,szeged/servo,nnethercote/servo,KiChjang/servo,pyfisch/servo,larsbergstrom/servo,szeged/servo,jimberlage/servo,fiji-flo/servo,saneyuki/servo,canaltinova/servo,sadmansk/servo,szeged/servo,peterjoel/servo,saneyuki/servo,pyfisch/servo,jimberlage/servo,emilio/servo,anthgur/servo,ConnorGBrewster/servo,ConnorGBrewster/servo,anthgur/servo,dati91/servo,mbrubeck/servo,mbrubeck/servo,pyfisch/servo,KiChjang/servo,paulrouget/servo,peterjoel/servo,DominoTree/servo,dati91/servo,KiChjang/servo,DominoTree/servo,nnethercote/servo,cbrewster/servo,canaltinova/servo,canaltinova/servo,dati91/servo,upsuper/servo,upsuper/servo,nnethercote/servo,saneyuki/servo,peterjoel/servo,larsbergstrom/servo,cbrewster/servo,mbrubeck/servo,pyfisch/servo,saneyuki/servo,mattnenterprise/servo,emilio/servo,szeged/servo,dati91/servo,splav/servo,fiji-flo/servo,larsbergstrom/servo,paulrouget/servo,jimberlage/servo,splav/servo,DominoTree/servo,nnethercote/servo,emilio/servo,notriddle/servo,jimberlage/servo,mattnenterprise/servo,saneyuki/servo,notriddle/servo,sadmansk/servo,mattnenterprise/servo,paulrouget/servo,ConnorGBrewster/servo,anthgur/servo,szeged/servo,dati91/servo,ConnorGBrewster/servo,fiji-flo/servo,larsbergstrom/servo,SimonSapin/servo,fiji-flo/servo,nnethercote/servo,mattnenterprise/servo,avadacatavra/servo,avadacatavra/servo,SimonSapin/servo,mbrubeck/servo,sadmansk/servo,szeged/servo,larsbergstrom/servo,KiChjang/servo,canaltinova/servo,SimonSapin/servo,KiChjang/servo,dati91/servo,cbrewster/servo,jimberlage/servo,pyfisch/servo,avadacatavra/servo,nnethercote/servo,cbrewster/servo,larsbergstrom/servo,pyfisch/servo,sadmansk/servo,avadacatavra/servo,DominoTree/servo,sadmansk/servo,saneyuki/servo,sadmansk/servo,larsbergstrom/servo,jimberlage/servo,upsuper/servo,saneyuki/servo,upsuper/servo,larsbergstrom/servo,ConnorGBrewster/servo,DominoTree/servo,KiChjang/servo,paulrouget/servo,KiChjang/servo,szeged/servo,peterjoel/servo,pyfisch/servo,splav/servo,mattnenterprise/servo,avadacatavra/servo,dati91/servo,peterjoel/servo,fiji-flo/servo,SimonSapin/servo,peterjoel/servo,anthgur/servo,paulrouget/servo,DominoTree/servo,KiChjang/servo,emilio/servo,notriddle/servo,canaltinova/servo,upsuper/servo,splav/servo,avadacatavra/servo,pyfisch/servo,canaltinova/servo,nnethercote/servo,mattnenterprise/servo,anthgur/servo,KiChjang/servo,ConnorGBrewster/servo,notriddle/servo,splav/servo,saneyuki/servo,peterjoel/servo,pyfisch/servo,upsuper/servo,fiji-flo/servo,emilio/servo,szeged/servo,SimonSapin/servo,paulrouget/servo,mbrubeck/servo,SimonSapin/servo,DominoTree/servo,cbrewster/servo,jimberlage/servo,fiji-flo/servo,anthgur/servo,upsuper/servo,notriddle/servo,SimonSapin/servo,emilio/servo,cbrewster/servo,emilio/servo,splav/servo,splav/servo,nnethercote/servo,avadacatavra/servo,mbrubeck/servo,ConnorGBrewster/servo,splav/servo,saneyuki/servo,splav/servo,peterjoel/servo,szeged/servo,saneyuki/servo,jimberlage/servo,notriddle/servo,mbrubeck/servo,DominoTree/servo,sadmansk/servo,ConnorGBrewster/servo,upsuper/servo,notriddle/servo,sadmansk/servo,paulrouget/servo,emilio/servo,anthgur/servo,cbrewster/servo,avadacatavra/servo,paulrouget/servo,notriddle/servo,dati91/servo,fiji-flo/servo,peterjoel/servo,KiChjang/servo,DominoTree/servo,jimberlage/servo,nnethercote/servo,notriddle/servo,larsbergstrom/servo,splav/servo,szeged/servo,mbrubeck/servo,emilio/servo,DominoTree/servo,mattnenterprise/servo,notriddle/servo,emilio/servo,anthgur/servo,mattnenterprise/servo,nnethercote/servo,pyfisch/servo,cbrewster/servo,paulrouget/servo,peterjoel/servo,canaltinova/servo,paulrouget/servo