Removed test assumptions about arrival order of status updates.
Removed test assumptions about arrival order of status updates.

Task status updates can arrive in any order. Adjusted the code to not
assume a particual order.

Review: https://reviews.apache.org/r/54422/

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