[maven] fix warnings

[dadoonet]

Some warnings appear in IntelliJ for the parent project:

The following variables are unknown. We should probably set them as properties. Note that every sub plugin or any user can overload those properties when running maven:

• ${project.parent.build.directory} (if #45 is merged)
• ${java.permGenSpace}
• ${forbidden.signatures}
• ${forbidden.test.signatures}
• ${scmBranch}
• ${validate.skip}
• ${validate.patternsFound}
• ${skipTests}
• ${plugin_classpath}
• ${runtime_classpath}
• ${test_classpath}

Also, it sounds like this plugin can not be found:

                <dependency>
                    <!--  must be on the classpath  -->
                    <groupId>org.jacoco</groupId>
                    <artifactId>org.jacoco.agent</artifactId>
                    <classifier>runtime</classifier>
                    <scope>test</scope>
                </dependency>

[rmuir]

Also, it sounds like this plugin can not be found:

There is nothing wrong with jacoco, its both declared in dependencyManagement, and works (if i do a jacoco profiling build of say kuromoji: mvn -Dtests.coverage=true test jacoco:report, then it produces target/site/jacoco with coverage report).

[dadoonet]

Yeah. Just that IntelliJ adds a warning on this part. Might be an issue in IntelliJ?