Enhance target JDK definition for JDK >= 9

[gnodet]

Defining maven.compiler.source and maven.compiler.target properties when
running on JDK >= 9 has some side effects.

Fixes #503
Follow-up on apache/maven-apache-parent#543 and apache/maven-apache-parent#550

[gnodet]

@slachiewicz @slawekjaranowski Note that those could be potentially moved to apache-parent if we want. Thoughts ?

[gnodet]

I've raised apache/maven-apache-parent#543 but we'll need to keep this PR.
The reason is that the apache parent only defines maven.compiler.source, maven.compiler.target, maven.compiler.release, and minimalJavaBuildVersion. The other properties are specific to the maven-parent, so we need this PR anyway.

[slawekjaranowski]

Looks too much complicated, as I mentioned in apache/maven-apache-parent#543
we should introduce on property lik javaVersion and only this one should be used in child project
maven.compiler.* should be only set in ASF parent and not used in childs

and then childs will not need an additional profiles

[slawekjaranowski]

can be simplified after:

• Introduce javaVersion property for maven.compiler.* configuration maven-apache-parent#551

[slawekjaranowski]

@gnodet I update to simply use javaVersion property