Test alerts do not run properly in some locales

[mcoles]

https://community.tableau.com/thread/334316

At present, the VizAlertsConfig workbook exports its CSV with the text "true" for the is_test column in English locales, but this is converted to "wahr" in German locales, which breaks the logic we have in vizalerts.py for picking up and running test alerts. This, and all other boolean values in the workbook, should be converted to integers with 0 / 1 options instead, and the code updated to look for them.