background callonce read causes scenarios to share variables
Failing test case here:

https://github.com/ericdriggs/karate-callonce-bug/blob/master/src/test/java/callonce-bug.feature

Expected:
* variables created by previous scenario remain undefined when another scenario starts

Actual
* variables still have previous values when start new scenario

Manually verified the following work correctly: karate.callSingle, callonce for a function variable