[MESOS-?]: Mesos POM generates to Jars, normal and shaded.

Updated the Mesos POM files [src/java/mesos.pom.in] to generate two jar
files. One will be the normal file and the other one will be the shaded
jar file that contains the _protobuf_ at the _org.apache.mesos.protobuf_
namespace.

[ticket: X] : ?

Author      : berngp
Reviewer    : ?
Testing     : ?