I solved it. Iinstead of using the maven-antrun-plugin I am now using the maven-surefire-report plugin along with the goal site maven-surefire:report . NOTE: You need to run the site goal first in order to generate the CSS files for the report.
<reporting>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-report-plugin</artifactId>
<version>2.16</version>
<configuration>
<showSuccess>false</showSuccess>
<outputDirectory>${basedir}/target/surefire-reports</outputDirectory>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-site-plugin</artifactId>
<version>2.1</version>
<configuration>
<outputDirectory>${basedir}/target/surefire-reports</outputDirectory>
</configuration>
</plugin>
</plugins>
</reporting>
</project>