[CI] Use 80 as a default port for previews

Summary:
The actual behavior is to not provide port translation if no port is specified, which is not very useful. Default to 80 (http) instead.
Since none of the currently supported websites are missing the port: config, there is no change in behavior.

Test Plan:

./contrib/teamcity/build-configurations.py preview-e.cash

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D13690