RFR: 8071566 Improve testing for multi-version JAR file maker tool

[Andrey Nazarov]

Hi,

Following tests for Jar tool were added:

Tests for API validator. Jar tool should detect API changes between releases. 
Test for custom manifest file. 
Test for version format in --release option 

Also refactoring of existing tests was made:
1. Common base class “MRTestBase.java” was extracted. 
2. Result and process builders were substituted by existing library classes jdk/test/lib/process/*

Please review.

Review: http://cr.openjdk.java.net/~anazarov/8071566/webrev.00/
Issue: https://bugs.openjdk.java.net/browse/JDK-8071566 <https://bugs.openjdk.java.net/browse/JDK-8071566>

—Andrey