[minor] [examples] Avoid packaging duplicate classes.

Add exclusions and explicit dependencies so that the examples
assembly does not duplicate classes already packaged in the main
assembly.

Also avoid relocating the commons-math3 package since it's already
a dependency of spark-core, and thus is already available in the
main assembly.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #5379 from vanzin/examples-deps and squashes the following commits:

12c258e [Marcelo Vanzin] [minor] [examples] Avoid re-packaging unneeded classes.

examples/pom.xml

@@ -90,6 +90,12 @@
       <groupId>org.apache.spark</groupId>
       <artifactId>spark-streaming-zeromq_${scala.binary.version}</artifactId>
       <version>${project.version}</version>
+      <exclusions>
+        <exclusion>
+          <groupId>org.spark-project.protobuf</groupId>
+          <artifactId>protobuf-java</artifactId>
+        </exclusion>
+      </exclusions>
     </dependency>
     <dependency>
       <groupId>org.apache.hbase</groupId>
@@ -234,6 +240,7 @@
     <dependency>
       <groupId>org.apache.commons</groupId>
       <artifactId>commons-math3</artifactId>
+      <scope>provided</scope>
     </dependency>
     <dependency>
       <groupId>com.twitter</groupId>
@@ -262,6 +269,22 @@
           <groupId>com.ning</groupId>
           <artifactId>compress-lzf</artifactId>
         </exclusion>
+        <exclusion>
+          <groupId>commons-cli</groupId>
+          <artifactId>commons-cli</artifactId>
+        </exclusion>
+        <exclusion>
+          <groupId>commons-codec</groupId>
+          <artifactId>commons-codec</artifactId>
+        </exclusion>
+        <exclusion>
+          <groupId>commons-lang</groupId>
+          <artifactId>commons-lang</artifactId>
+        </exclusion>
+        <exclusion>
+          <groupId>commons-logging</groupId>
+          <artifactId>commons-logging</artifactId>
+        </exclusion>
         <exclusion>
           <groupId>io.netty</groupId>
           <artifactId>netty</artifactId>
@@ -270,10 +293,22 @@
           <groupId>jline</groupId>
           <artifactId>jline</artifactId>
         </exclusion>
+        <exclusion>
+          <groupId>net.jpountz.lz4</groupId>
+          <artifactId>lz4</artifactId>
+        </exclusion>
         <exclusion>
           <groupId>org.apache.cassandra.deps</groupId>
           <artifactId>avro</artifactId>
         </exclusion>
+        <exclusion>
+          <groupId>org.apache.commons</groupId>
+          <artifactId>commons-math3</artifactId>
+        </exclusion>
+        <exclusion>
+          <groupId>org.apache.thrift</groupId>
+          <artifactId>libthrift</artifactId>
+        </exclusion>
       </exclusions>
     </dependency>
     <dependency>
@@ -281,6 +316,17 @@
       <artifactId>scopt_${scala.binary.version}</artifactId>
       <version>3.2.0</version>
     </dependency>
+
+    <!--
+      The following dependencies are already present in the Spark assembly, so we want to force
+      them to be provided.
+    -->
+    <dependency>
+      <groupId>org.scala-lang</groupId>
+      <artifactId>scala-library</artifactId>
+      <scope>provided</scope>
+    </dependency>
+
   </dependencies>
 
   <build>
@@ -322,12 +368,6 @@
               </excludes>
             </filter>
           </filters>
-          <relocations combine.children="append">
-            <relocation>
-              <pattern>org.apache.commons.math3</pattern>
-              <shadedPattern>org.spark-project.commons.math3</shadedPattern>
-            </relocation>
-          </relocations>
           <transformers>
             <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer" />
             <transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">