[SUREFIRE-2070] can not set line.separator

**[pengningjun](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=copbint)** opened **[SUREFIRE-2070](https://issues.apache.org/jira/browse/SUREFIRE-2070?redirect=false)** and commented

If we try to set line.separator by {**}systemPropertyVariables{**}, there will be a WARN：[code](https://github.com/apache/maven-surefire/blob/master/maven-surefire-common/src/main/java/org/apache/maven/plugin/surefire/SurefireProperties.java#L50)。

So I try to set line.separator by **argLine** but finally found '\r' and '\n' is replaced: [code](https://github.com/apache/maven-surefire/blob/f6be3e648938414b222b50907b1db2d6a3cc977b/maven-surefire-common/src/main/java/org/apache/maven/plugin/surefire/booterclient/DefaultForkConfiguration.java#L256)

So what is the right way to set line.separator?

Any suggestion will be great appreciated!

---
No further details from [SUREFIRE-2070](https://issues.apache.org/jira/browse/SUREFIRE-2070?redirect=false)

Start with maven-surefire-common/src/main/java/org/apache/maven/plugin/surefire/SurefireProperties.java and DefaultForkConfiguration.java, especially the systemPropertyVariables warning and argLine processing described in the report. Determine how line.separator is currently handled and document or verify the supported way to configure it. Done means the configuration behavior is clear and the reported replacement problem is addressed or reproduced with coverage.

Written by the indexing model from the issue text.