Various test failures in impl-maven-embedded on Windows

Building the project in this environment:

$ ./mvnw -version
Apache Maven 3.5.2 (138edd61fd100ec658bfa2d307c43b76940a5d7d; 2017-10-18T09:58:13+02:00)
Maven home: C:\Users\Falko\.m2\wrapper\dists\apache-maven-3.5.2-bin\28qa8v9e2mq69covern8vmdkj0\apache-maven-3.5.2
Java version: 1.8.0_202, vendor: Oracle Corporation
Java home: C:\_dev\Java\jdk1.8.0_202\jre
Default locale: de_DE, platform encoding: Cp1252
OS name: "windows 10", version: "10.0", arch: "amd64", family: "windows"

yields multiple test failures which can be broken down into two cause categories:

• log output matching with / instead of File.separatorChar
• failing clean due to still opened jar files (Windows is very picky about that)

The second category is mainly caused by Shrinkwrap leaving ZipFile objects open after they have been parsed into Archives (which makes sense if you'd want to modify them) in combination with each test operating on the same test project in src/it.
The second aspect is not a good idea in terms of test separation, either.