Fixed `mesos-execute` help text related to task resources.
Fixed `mesos-execute` help text related to task resources.

With reservation refinement, `mesos-execute` requires input resources
to be in the post-reservation-refinement format. This patch updates
the help string to reflect this correctly.

Review: https://reviews.apache.org/r/61253/

zmalik/mesos,jpeach/mesos,andschwa/mesos,abudnik/mesos,zmalik/mesos,zmalik/mesos,dforsyth/mesos,asamerh4/mesos,Gilbert88/mesos,gsantovena/mesos,gsantovena/mesos,andschwa/mesos,jpeach/mesos,dforsyth/mesos,chhsia0/mesos,verizonlabs/mesos,verizonlabs/mesos,gsantovena/mesos,kaysoky/mesos,reneploetz/mesos,kaysoky/mesos,asamerh4/mesos,jpeach/mesos,abudnik/mesos,abudnik/mesos,Gilbert88/mesos,dforsyth/mesos,Gilbert88/mesos,andschwa/mesos,gsantovena/mesos,asamerh4/mesos,verizonlabs/mesos,chhsia0/mesos,kaysoky/mesos,andschwa/mesos,reneploetz/mesos,asamerh4/mesos,Gilbert88/mesos,chhsia0/mesos,chhsia0/mesos,verizonlabs/mesos,gsantovena/mesos,Gilbert88/mesos,zmalik/mesos,kaysoky/mesos,kaysoky/mesos,andschwa/mesos,zmalik/mesos,reneploetz/mesos,reneploetz/mesos,chhsia0/mesos,jpeach/mesos,jpeach/mesos,reneploetz/mesos,reneploetz/mesos,dforsyth/mesos,verizonlabs/mesos,chhsia0/mesos,dforsyth/mesos,verizonlabs/mesos,kaysoky/mesos,abudnik/mesos,chhsia0/mesos,andschwa/mesos,gsantovena/mesos,dforsyth/mesos,verizonlabs/mesos,abudnik/mesos,Gilbert88/mesos,zmalik/mesos,asamerh4/mesos,gsantovena/mesos,abudnik/mesos,asamerh4/mesos,asamerh4/mesos,jpeach/mesos,dforsyth/mesos,andschwa/mesos,Gilbert88/mesos,reneploetz/mesos,abudnik/mesos,jpeach/mesos,kaysoky/mesos,zmalik/mesos