Cleaned up `using` statements.
Cleaned up `using` statements.

Review: https://reviews.apache.org/r/55304/

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