Implemented `status` method in `ComposingContainerizer`.
Implemented `status` method in `ComposingContainerizer`.

This method will be used by the agent to retrieve `ContainerStatus` from
the `Containerizer`, that was responsible for launching the container.

Review: https://reviews.apache.org/r/43565/

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