Fail fast ITs if not on Windows

[fmallet]

Currently, MetricsTest will fail if not running on Windows because the C# sensor doesn't run.
Unfortunately there is only a log in debug (not activated by default) that gives a hint about why it fails.
ITs should fail immediately if not running on Windows, with a clear message about the reason.

[Evangelink]

@henryju @dbmeneses @janos-ss It seems like the impacted class is this one https://github.com/SonarSource/sonar-csharp/blob/master/its/src/test/java/com/sonar/it/csharp/MetricsTest.java what is the recommended way to detect the OS on a test in Java?

[dbmeneses]

You can do the same as the sensor itself is doing: if (!SystemUtils.IS_OS_WINDOWS) { LOG.debug("OS is not Windows. Skip Sensor."); return false; } (and here the log should be changed to info or warn).

[dbmeneses]

You might need to add the library apache commons lang to the ITs (I don't know if it is already there). https://mvnrepository.com/artifact/org.apache.commons/commons-lang3/3.6