Fix a race in ActionCable stream tests
Fix a race in ActionCable stream tests

These tests double-stub connection.pubsub, so we need to ensure the
first call's completed before we set up for the second.

MSP-Greg/rails,Envek/rails,EmmaB/rails-1,Erol/rails,yawboakye/rails,yhirano55/rails,felipecvo/rails,joonyou/rails,baerjam/rails,hanystudy/rails,gfvcastro/rails,EmmaB/rails-1,mathieujobin/reduced-rails-for-travis,mtsmfm/railstest,fabianoleittes/rails,BlakeWilliams/rails,illacceptanything/illacceptanything,kirs/rails-1,bogdanvlviv/rails,bradleypriest/rails,ttanimichi/rails,mathieujobin/reduced-rails-for-travis,tjschuck/rails,yhirano55/rails,arunagw/rails,Vasfed/rails,xlymian/rails,mijoharas/rails,ngpestelos/rails,pschambacher/rails,yahonda/rails,Sen-Zhang/rails,utilum/rails,ttanimichi/rails,printercu/rails,eileencodes/rails,tgxworld/rails,georgeclaghorn/rails,riseshia/railsguides.kr,prathamesh-sonpatki/rails,iainbeeston/rails,rails/rails,bogdanvlviv/rails,riseshia/railsguides.kr,palkan/rails,gauravtiwari/rails,riseshia/railsguides.kr,printercu/rails,yawboakye/rails,mtsmfm/railstest,deraru/rails,Erol/rails,betesh/rails,prathamesh-sonpatki/rails,mohitnatoo/rails,gfvcastro/rails,eileencodes/rails,hanystudy/rails,utilum/rails,utilum/rails,repinel/rails,baerjam/rails,Erol/rails,samphilipd/rails,ngpestelos/rails,tgxworld/rails,rafaelfranca/omg-rails,notapatch/rails,iainbeeston/rails,yalab/rails,illacceptanything/illacceptanything,deraru/rails,matrinox/rails,Sen-Zhang/rails,kamipo/rails,aditya-kapoor/rails,assain/rails,matrinox/rails,MSP-Greg/rails,pschambacher/rails,flanger001/rails,maicher/rails,rossta/rails,samphilipd/rails,brchristian/rails,xlymian/rails,aditya-kapoor/rails,maicher/rails,ledestin/rails,kaspth/rails,lcreid/rails,aditya-kapoor/rails,Edouard-chin/rails,palkan/rails,kddeisz/rails,BlakeWilliams/rails,flanger001/rails,mohitnatoo/rails,baerjam/rails,iainbeeston/rails,odedniv/rails,marklocklear/rails,joonyou/rails,tgxworld/rails,prathamesh-sonpatki/rails,MSP-Greg/rails,illacceptanything/illacceptanything,vipulnsward/rails,joonyou/rails,illacceptanything/illacceptanything,yhirano55/rails,brchristian/rails,rails/rails,illacceptanything/illacceptanything,flanger001/rails,georgeclaghorn/rails,jeremy/rails,untidy-hair/rails,yahonda/rails,yahonda/rails,yasslab/railsguides.jp,utilum/rails,pvalena/rails,BlakeWilliams/rails,assain/rails,repinel/rails,Stellenticket/rails,Edouard-chin/rails,eileencodes/rails,kamipo/rails,starknx/rails,vipulnsward/rails,printercu/rails,notapatch/rails,lucasmazza/rails,ttanimichi/rails,untidy-hair/rails,repinel/rails,kddeisz/rails,koic/rails,betesh/rails,untidy-hair/rails,fabianoleittes/rails,lucasmazza/rails,Stellenticket/rails,alecspopa/rails,aditya-kapoor/rails,brchristian/rails,esparta/rails,alecspopa/rails,illacceptanything/illacceptanything,starknx/rails,georgeclaghorn/rails,kmayer/rails,mechanicles/rails,gauravtiwari/rails,kmcphillips/rails,kddeisz/rails,esparta/rails,koic/rails,mijoharas/rails,mechanicles/rails,rails/rails,illacceptanything/illacceptanything,pvalena/rails,Vasfed/rails,rails/rails,ledestin/rails,hanystudy/rails,starknx/rails,felipecvo/rails,illacceptanything/illacceptanything,rafaelfranca/omg-rails,Envek/rails,vipulnsward/rails,illacceptanything/illacceptanything,travisofthenorth/rails,lcreid/rails,kddeisz/rails,rossta/rails,untidy-hair/rails,mohitnatoo/rails,Edouard-chin/rails,kmcphillips/rails,odedniv/rails,schuetzm/rails,Stellenticket/rails,illacceptanything/illacceptanything,illacceptanything/illacceptanything,yalab/rails,illacceptanything/illacceptanything,georgeclaghorn/rails,shioyama/rails,kmcphillips/rails,yawboakye/rails,fabianoleittes/rails,illacceptanything/illacceptanything,Vasfed/rails,assain/rails,yalab/rails,schuetzm/rails,arunagw/rails,fabianoleittes/rails,joonyou/rails,iainbeeston/rails,vipulnsward/rails,ngpestelos/rails,bradleypriest/rails,jeremy/rails,xlymian/rails,kamipo/rails,yasslab/railsguides.jp,kmayer/rails,BlakeWilliams/rails,EmmaB/rails-1,pvalena/rails,gfvcastro/rails,yasslab/railsguides.jp,mohitnatoo/rails,deraru/rails,assain/rails,kaspth/rails,lucasmazza/rails,Sen-Zhang/rails,gcourtemanche/rails,gcourtemanche/rails,mechanicles/rails,deraru/rails,alecspopa/rails,mtsmfm/railstest,mechanicles/rails,gauravtiwari/rails,bogdanvlviv/rails,eileencodes/rails,tjschuck/rails,Envek/rails,travisofthenorth/rails,Vasfed/rails,mijoharas/rails,shioyama/rails,maicher/rails,lcreid/rails,illacceptanything/illacceptanything,yahonda/rails,kaspth/rails,samphilipd/rails,jeremy/rails,repinel/rails,palkan/rails,yalab/rails,kirs/rails-1,felipecvo/rails,odedniv/rails,kmcphillips/rails,marklocklear/rails,MSP-Greg/rails,riseshia/railsguides.kr,gcourtemanche/rails,palkan/rails,matrinox/rails,yasslab/railsguides.jp,ledestin/rails,printercu/rails,flanger001/rails,yawboakye/rails,tgxworld/rails,koic/rails,pschambacher/rails,esparta/rails,travisofthenorth/rails,pvalena/rails,mathieujobin/reduced-rails-for-travis,schuetzm/rails,notapatch/rails,tjschuck/rails,illacceptanything/illacceptanything,kmayer/rails,lcreid/rails,betesh/rails,Envek/rails,shioyama/rails,marklocklear/rails,rafaelfranca/omg-rails,arunagw/rails,yhirano55/rails,Erol/rails,shioyama/rails,jeremy/rail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