Mesos-slave --help should not return as failed.
Mesos-slave --help should not return as failed.

Doing a simple \`mesos-agent --help\` should return with exit_status=0.
It's not the case since work_dir is considered as mandatory.

Review: https://reviews.apache.org/r/50570/

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