Added authorization tests of launching container sessions API.
Added authorization tests of launching container sessions API.

Introduced a test which ensures that unauthorized users are unable to
launch nested container sessions.

Review: https://reviews.apache.org/r/54783/

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