Handling test_framework's initial state assumptions

# Issue
When I run scenarios that were built for Bitcoin Core's functional test framework, I get errors relating to wallet balance issues.

# Cause
Core's functional test framework has a non-empty initial state. For example, it begins by populating the blockchain by default. This means that users of the framework write code that relies on the existence of blocks and wallets that already have coins.

# Possible solutions
Recreate the functional test's initial state in Warnet, and then ...
A. ...allow users to explicitly run scenarios within that initial state by using command line flags.
B. ...implicitly create the state for any scenarios that live a specified folder.
C. ...scenario authors explicitly create the state by providing a hook that they manually add to any scenario that needs it.