HBASE-18697 (addendum) Add "o.a.h.h.mapreduce.Driver" as main class to hbase-shaded-mapreduce jar.

Without it, following command fails.
bin/hadoop jar <jar> rowcouter <table>
In general, the 'program names' won't work. One would have needed to specify class name explicitly otherwise.

Change-Id: Ib94cca5e9fc45b19436b7ae0d6634de097572537

hbase-shaded/hbase-shaded-mapreduce/pom.xml

@@ -45,6 +45,20 @@
                     <skipAssembly>true</skipAssembly>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-jar-plugin</artifactId>
+                <configuration>
+                    <archive>
+                        <manifest>
+                            <!--Include the Driver class as the 'main'.
+                                 Executing the jar will then show a list of the basic MR jobs.
+                                 -->
+                            <mainClass>org/apache/hadoop/hbase/mapreduce/Driver</mainClass>
+                        </manifest>
+                    </archive>
+                </configuration>
+            </plugin>
         </plugins>
     </build>
     <dependencies>