Refactored protobuf::read to return the protobuf (instead of bool).

From: Ben Mahler <benjamin.mahler@gmail.com>
Review: https://reviews.apache.org/r/8696

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1440848 13f79535-47bb-0310-9956-ffa450edef68
Fixed regression in 'make clean' for Hadoop.

From: Ben Mahler <benjamin.mahler@gmail.com>
Review: https://reviews.apache.org/r/8686

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1440849 13f79535-47bb-0310-9956-ffa450edef68