Rename buildbot teamcity wrapper module

Summary:
Installing the teamcity-messages pip package includes a module named teamcity.
This conflicts with our own teamcity wrapper module, so rename it accordingly.
This patch will allow us to run buildbot tests using build-configurations.py.

Test Plan:

cd contrib/buildbot/test
workon abcbot
pip3 install teamcity-messages deepmerge pytest
pip3 install -r ../requirements.txt
pytest

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7364