[mock-chronik-client] Install mock-chronik-client dependencies before running tests that require them

Summary: Install mock-chronik-client deps before running js-mocha test suite in repo that depends on them

Test Plan:
Test on js-mocha suite that does not require mock-chronik-client: ./contrib/teamcity/build-configurations.py ecashaddrjs-tests
Test on js-mocha suite that does require mock-chronik-client: ./contrib/teamcity/build-configurations.py ecash-herald-tests

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15615