Fixed help string for "--attributes" flag.
Fixed help string for "--attributes" flag.

Review: https://reviews.apache.org/r/24840

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