[FLINK-8383][mesos] Disable test-jar shading

This closes #5258.

flink-mesos/pom.xml

@@ -262,6 +262,7 @@ under the License.
 							<goal>shade</goal>
 						</goals>
 						<configuration>
+							<shadeTestJar>false</shadeTestJar>
 							<artifactSet>
 								<includes combine.children="append">
 									<include>com.google.protobuf:protobuf-java</include>