Revert "Stop using mvn to initialize/update submodule"

This reverts commit 121a19c.

Author: oschwald

pom.xml

@@ -199,6 +199,24 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>exec-maven-plugin</artifactId>
+                <version>3.0.0</version>
+                <executions>
+                    <execution>
+                        <phase>initialize</phase>
+                        <id>invoke build</id>
+                        <goals>
+                            <goal>exec</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <executable>git</executable>
+                    <commandlineArgs>submodule update --init --recursive</commandlineArgs>
+                </configuration>
+            </plugin>
             <plugin>
                 <groupId>org.codehaus.mojo</groupId>
                 <artifactId>versions-maven-plugin</artifactId>