Allow to reference build files from the classpath

          <plugin>
            <groupId>org.nuxeo.build</groupId>
            <artifactId>ant-assembly-maven-plugin</artifactId>
            <dependencies>
              <dependency>
                <groupId>org.nuxeo</groupId>
                <artifactId>nuxeo-qa-tools</artifactId>
                <version>2.0</version>
              </dependency>
            </dependencies>
            (...)
                <configuration>
                  <buildFiles>
                    <buildFile>classpath:integration/vcstests.xml</buildFile>
                  </buildFiles>
            (...)
          </plugin>