Let the check style bind to maven process-sources life cycle. (#2683)

pom.xml

@@ -17,7 +17,8 @@
   ~
   -->
 
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
 
     <groupId>org.apache.skywalking</groupId>
@@ -28,7 +29,7 @@
         <groupId>org.apache</groupId>
         <artifactId>apache</artifactId>
         <version>21</version>
-        <relativePath />
+        <relativePath/>
     </parent>
 
     <modules>
@@ -464,16 +465,11 @@
                         <artifactId>apm-checkstyle</artifactId>
                         <version>6.0.0-GA</version>
                     </dependency>
-                    <dependency>
-                        <groupId>com.puppycrawl.tools</groupId>
-                        <artifactId>checkstyle</artifactId>
-                        <version>8.11</version>
-                    </dependency>
                 </dependencies>
                 <executions>
                     <execution>
                         <id>validate</id>
-                        <phase>validate</phase>
+                        <phase>process-sources</phase>
                         <configuration>
                             <configLocation>skywalking/checkStyle.xml</configLocation>
                             <headerLocation>skywalking/CHECKSTYLE_HEAD</headerLocation>
@@ -481,9 +477,15 @@
                             <consoleOutput>true</consoleOutput>
                             <includeTestSourceDirectory>true</includeTestSourceDirectory>
                             <failsOnError>true</failsOnError>
-                            <excludes>org.apache.skywalking.apm/network/**/*.java,
-                                org.apache.skywalking.apm/collector/remote/grpc/**/*.java,
-                                org.apache.skywalking.apm/agent/core/context/ids/base64/*.java
+                            <includes>org/apache/skywalking/**/*.java</includes>
+                            <excludes>
+                                org/apache/skywalking/apm/network/register/v2/**/*.java,
+                                org/apache/skywalking/apm/network/common/**/*.java,
+                                org/apache/skywalking/apm/network/servicemesh/**/*.java,
+                                org/apache/skywalking/apm/network/language/**/*.java,
+                                org/apache/skywalking/oap/server/core/remote/grpc/proto/*.java,
+                                org/apache/skywalking/oal/tool/grammar/*.java,
+                                org/apache/skywalking/oap/server/exporter/grpc/*.java
                             </excludes>
                         </configuration>
                         <goals>