[Cashtab] Improve and standardize CreateToken tests

Summary:
T3444

Use standardized wrapper for CreateToke and CreateToken tests. Refactor and improve tests to work with new wrapper.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15482