[CMAKE] Allow to run boost unit tests in parallel

Summary:
This is inspired from the autotools equivalent, ported in D3535.
The idea is to run each test in it's own process by passing it to the
boost test filter. Then it relies on ninja to run them in parallel.

This implies the removal of ctest.

Test Plan:

cmake -GNinja ..
ninja check-all

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4698