Fixed typos in master endpoint help messages.
Fixed typos in master endpoint help messages.

Review: https://reviews.apache.org/r/37252

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