Avoided sending an inconsistent `TaskInfo` to the allocator.
Avoided sending an inconsistent `TaskInfo` to the allocator.

Since we drop invalid tasks on a `LAUNCH` operation, we send a new
`Operation` with only the valid tasks appended. At the same time,
we adjust the `TaskInfo` a little bit to perform validation, and
to maintain backwards compatibility. However, the unmodified
`TaskInfo` was sent to the allocator. Since the allocator does not
look at the modified fields, this was inconsequential, but we should
avoid sending inconsistent `TaskInfo`s in general.

We also avoided creating an unnecessary copy of the `TaskInfo`.

Review: https://reviews.apache.org/r/60281

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