Allow access to any exec_output in a rule

[JordanSussman]

This would allow you to cover scenario where you want to access output of multiple execs individually

[wass3r]

currently, exec_output is overwritten by the last output of an exec action. the ask is to come up with a solution to be able to access the output of any exec action in a rule.

[wass3r]

couple of solutions:

1. reassign output to a different user-defined variable
2. use other action property, ie. name to namespace the output
3. add global mechanism to assign something to a user-defined variable

other thoughts?