Add Maven Javadoc Plugin configuration to exclude non-essential Apache Geode packages.

The Jenskins CI build is producing Javadoc errors/warnings of the nature:

20:55:04  [ERROR] Failed to execute goal org.apache.maven.plugins:maven-javadoc-plugin:3.2.0:jar (package-javadoc) on project spring-data-geode: MavenReportException: Error while generating Javadoc:
20:55:04  [ERROR] Exit code: 1 - /opt/jenkins/data/workspace/spring-data-geode_3.0.x/spring-data-geode/src/main/java/org/springframework/data/gemfire/client/GemfireDataSourcePostProcessor.java:26: error: cannot find symbol
20:55:04  [ERROR] import org.apache.geode.management.internal.cli.functions.GetRegionsFunction;
20:55:04  [ERROR]                                                          ^
20:55:04  [ERROR]   symbol:   class GetRegionsFunction
20:55:04  [ERROR]   location: package org.apache.geode.management.internal.cli.functions
20:55:04  [ERROR] /opt/jenkins/data/workspace/spring-data-geode_3.0.x/spring-data-geode/src/main/java/org/springframework/data/gemfire/config/admin/remote/FunctionGemfireAdminTemplate.java:31: error: cannot find symbol
20:55:04  [ERROR] import org.apache.geode.management.internal.cli.functions.GetRegionsFunction;
20:55:04  [ERROR]                                                          ^
20:55:04  [ERROR]   symbol:   class GetRegionsFunction
20:55:04  [ERROR]   location: package org.apache.geode.management.internal.cli.functions
20:55:04  [ERROR] /opt/jenkins/data/workspace/spring-data-geode_3.0.x/spring-data-geode/src/main/java/org/springframework/data/gemfire/function/PojoFunctionWrapper.java:53: error: cannot access Identifiable
20:55:04  [ERROR] public class PojoFunctionWrapper implements Function {
20:55:04  [ERROR]        ^
20:55:04  [ERROR]   class file for org.apache.geode.lang.Identifiable not found
20:55:04  [ERROR] warning: unknown enum constant When.MAYBE
20:55:04  [ERROR]   reason: class file for javax.annotation.meta.When not found
20:55:04  [ERROR] 3 errors
20:55:04  [ERROR] 1 warning

Resolves gh-538.

Author: jxblum

Diff for: spring-data-geode/pom.xml

@@ -286,6 +286,13 @@
 					</systemProperties>
 				</configuration>
 			</plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-javadoc-plugin</artifactId>
+				<configuration>
+					<excludePackageNames>org.apache.geode.lang:org.apache.geode.management.internal</excludePackageNames>
+				</configuration>
+			</plugin>
 		</plugins>
 	</build>