Changed the signature of a DefaultExecutor kill method.
Changed the signature of a DefaultExecutor kill method.

This method is being passed the container to be killed as
`Owned<Container>`.

The container object is owned by the executor and stored
in `LinkedHashMap<TaskID, Owner<Container>> containers`.

We should pass around raw pointers and not make copies of
the stored `Owned` object, so this patch changes the
signature of the `kill` method.

Review: https://reviews.apache.org/r/65692/

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