Updated a few comments in MesosContainerizer.
Updated a few comments in MesosContainerizer.

Review: https://reviews.apache.org/r/51418

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