POM configurado para criar um diretório com o plugin AntRun.

pom.xml

<project ...>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-antrun-plugin</artifactId>
        <version>1.8</version>
        <executions>
          <execution>
            <id>create-report-folder</id>
            <phase>initialize</phase>
            <configuration>
              <tasks>
                <mkdir dir="report" />
              </tasks>  
            </configuration>
            <goals>
              <goal>run</goal>
            </goals>  
          </execution>  
        </executions>  
      </plugin>  
    </plugins>  
  </build>  
  ...
</project>