ZOOKEEPER-3028 add release plugin

pom.xml

@@ -66,7 +66,7 @@
   </modules>
 
   <scm>
-    <connection>scm:git:git://git.apache.org/zookeeper.git</connection>
+    <connection>scm:git:https://gitbox.apache.org/repos/asf/zookeeper.git</connection>
     <developerConnection>scm:git:https://gitbox.apache.org/repos/asf/zookeeper.git</developerConnection>
     <url>https://gitbox.apache.org/repos/asf/zookeeper.git</url>
   </scm>
@@ -447,6 +447,16 @@
           <artifactId>maven-assembly-plugin</artifactId>
           <version>3.1.0</version>
         </plugin>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-gpg-plugin</artifactId>
+          <version>1.6</version>
+        </plugin>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-release-plugin</artifactId>
+          <version>2.5.3</version>
+        </plugin>
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-surefire-plugin</artifactId>
@@ -630,6 +640,20 @@
         <groupId>com.github.spotbugs</groupId>
         <artifactId>spotbugs-maven-plugin</artifactId>
       </plugin>
+
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-gpg-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>sign-artifacts</id>
+            <phase>verify</phase>
+            <goals>
+              <goal>sign</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>