Add possibility to save System properties among with maven prooperties to file.

[kool79]

Currently we can overrride maven property with system property with
mvn -Dprop.name=updatedValuevalue
Plugin saves such property (prop.name) to file only when such property defined in section of maven. If does not contain prop.name then output file will not contain it also.
This behavior forces me to define all properties inside maven but it is not convinient in my case. I just want to pass-through properties from and from maven CLI to samoe extarnal file which will be used later (by my tests). Test has too many different input parameters and I dont want to change pom file every time when I introduce new param.

[oarkhipov]

I've bumped to the same requiremetns. It looks like a bug. In IDEA i have many profiles, but in Jenkis build it's more convinient to use system props.