Added benchmark for allocator metrics.
Added benchmark for allocator metrics.

Review: https://reviews.apache.org/r/44853/

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