[electrum] install also the basic dependencies when running functional tests

Summary: The job is not necessarily going to run on a fully configured machine with all the dependencies installed.

Test Plan:

./contrib/teamcity/build-configurations.py electrum-functional-tests

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14277