[iguana] Run the tests as part of ninja check

Summary: Just like any other bitcoin-x tools. This also makes it simpler to run on various platforms and build conditions.

Test Plan:

ninja check

Make sure the iguana suite is ran.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16836