Added task labels modeling to http helpers.
Added task labels modeling to http helpers.

Review: https://reviews.apache.org/r/28155

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