Create function varsToProps(| separated varNamess, | separated propNames) to simplify passing data from setUp thread group

**Sebb** ([Bug 53795](https://bz.apache.org/bugzilla//show_bug.cgi?id=53795&redirect=false)):
Variables can be defined in a setUp thread group. These can be saved as properties so they can be referenced in subsequent thread groups.

However it's currently quite awkward saving variables as properties.

It would be useful to add a test element that was able to save a list of variables as properties.

Alternatively or additionally, it might be useful to be able to provide a list of variables that are copied from the setUp group to subsequent thread groups.

Votes in Bugzilla: 1
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