Added test `ReservationTest.PreventUnreservingAlienResources`.
Added test `ReservationTest.PreventUnreservingAlienResources`.

This test ensures that a framework can't use an `UNRESERVE` operation to
steal resources reserved by a framework with another role.

Review: https://reviews.apache.org/r/53534/

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