javaHome parameter is ignored and inherited unexpectedly

The release: mojos have a configuration <javaHome> which defaults to ${java.home}. From reading the documentation it seems like this is used to propagate the JAVA version of the parent process to the invoked build of prepare and perform. This inheritance is important in order to properly support compiles. The documentation does not mention that the option is ignored.

The following proposed patch might be able to solve the problem by setting the JAVA_HOME variable as documented. This also helps some situations where CI servers not reliable replicate builds.

The patch does not include it, but most likely it should also be noted that MAVEN_SKIP_RC=true should be added to the child's env.

https://github.com/apache/maven-release/pull/5