Allowed setting role in `mesos-execute`.
Allowed setting role in `mesos-execute`.

Review: https://reviews.apache.org/r/43935/

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