Clean cache and tmp directory for instegration tests

Summary: As per title.

Test Plan:

ninja clean
ls test

Verify that tmp and cache are gone.

Reviewers: #bitcoin_abc, jasonbcox, Fabien

Reviewed By: #bitcoin_abc, jasonbcox, Fabien

Subscribers: jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D5681