[CI] Generate Junit output for the cashtab tests

Summary:
This integrates the cashtab tests with Teamcity.

Depends on D8824 and D8828.

Test Plan:

./contrib/teamcity/build-configurations.py cashtab-tests

Check the abc-ci-builds/cashtab-tests/artifacts/junit/cashtab.xml report
is generated.

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8832