HBASE-27478 [hbase-thirdparty] Use maven flatten plugin to generate final pom (#96)

Signed-off-by: Xin Sun <ddupgs@gmail.com>
diff --git a/.gitignore b/.gitignore
index e3e7e99..4ccbf38 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 .classpath
 .idea
 *.iml
+.flattened-pom.xml
diff --git a/pom.xml b/pom.xml
index a1527bc..92f5171 100644
--- a/pom.xml
+++ b/pom.xml
@@ -350,6 +350,32 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>flatten-maven-plugin</artifactId>
+        <version>1.3.0</version>
+        <configuration>
+          <embedBuildProfileDependencies>true</embedBuildProfileDependencies>
+        </configuration>
+        <executions>
+          <!-- enable flattening -->
+          <execution>
+            <id>flatten</id>
+            <goals>
+              <goal>flatten</goal>
+            </goals>
+            <phase>process-resources</phase>
+          </execution>
+          <!-- ensure proper cleanup -->
+          <execution>
+            <id>flatten.clean</id>
+            <goals>
+              <goal>clean</goal>
+            </goals>
+            <phase>clean</phase>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>
   <!--These are the third-party libs we want to relocate-->