FetcherTests: Use ASSERT instead of EXPECT if the subsequent logic relies on the outcome.
FetcherTests: Use ASSERT instead of EXPECT if the subsequent logic relies on the outcome.

Fixes MESOS-3171.

Review: https://reviews.apache.org/r/36889

dforsyth/mesos,neilconway/mesos,kaysoky/mesos,chhsia0/mesos,craimbert/mesos,jpeach/mesos,kaysoky/mesos,kaysoky/mesos,zmalik/mesos,kaysoky/mesos,craimbert/mesos,chhsia0/mesos,chhsia0/mesos,dforsyth/mesos,verizonlabs/mesos,reneploetz/mesos,jpeach/mesos,asamerh4/mesos,gsantovena/mesos,verizonlabs/mesos,Gilbert88/mesos,andschwa/mesos,Aman-Jain-14/customizedMesos,zmalik/mesos,chhsia0/mesos,neilconway/mesos,andschwa/mesos,jpeach/mesos,chhsia0/mesos,reneploetz/mesos,abudnik/mesos,dforsyth/mesos,abudnik/mesos,neilconway/mesos,yuquanshan/customizedMesos,zmalik/mesos,neilconway/mesos,Aman-Jain-14/customizedMesos,gsantovena/mesos,verizonlabs/mesos,gsantovena/mesos,dforsyth/mesos,gsantovena/mesos,jpeach/mesos,chhsia0/mesos,Gilbert88/mesos,yuquanshan/customizedMesos,reneploetz/mesos,andschwa/mesos,dforsyth/mesos,Aman-Jain-14/customizedMesos,kaysoky/mesos,abudnik/mesos,Gilbert88/mesos,verizonlabs/mesos,zmalik/mesos,reneploetz/mesos,gsantovena/mesos,asamerh4/mesos,craimbert/mesos,zmalik/mesos,yuquanshan/customizedMesos,asamerh4/mesos,gsantovena/mesos,andschwa/mesos,abudnik/mesos,andschwa/mesos,asamerh4/mesos,craimbert/mesos,reneploetz/mesos,craimbert/mesos,zmalik/mesos,yuquanshan/customizedMesos,asamerh4/mesos,Gilbert88/mesos,zmalik/mesos,dforsyth/mesos,neilconway/mesos,kaysoky/mesos,craimbert/mesos,jpeach/mesos,jpeach/mesos,kaysoky/mesos,asamerh4/mesos,neilconway/mesos,reneploetz/mesos,gsantovena/mesos,yuquanshan/customizedMesos,Gilbert88/mesos,Gilbert88/mesos,chhsia0/mesos,abudnik/mesos,asamerh4/mesos,dforsyth/mesos,Gilbert88/mesos,yuquanshan/customizedMesos,verizonlabs/mesos,Aman-Jain-14/customizedMesos,jpeach/mesos,andschwa/mesos,Aman-Jain-14/customizedMesos,neilconway/mesos,verizonlabs/mesos,abudnik/mesos,andschwa/mesos,Aman-Jain-14/customizedMesos,craimbert/mesos,abudnik/mesos,verizonlabs/mesos,reneploetz/mesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos