Zanata stats tool: improve speed with user API
Zanata stats tool: improve speed with user API

This patch enhances the speed of Zanata stats by using
user-based Zanata APIs rather than project-based APIs,
which took >1 days as more Zanata users and translation data
were accumulated.

Note that the API scheme follows with Stackalytics
: https://opendev.org/x/stackalytics/src/branch/master/stackalytics/processor/zanata.py#L38

Change-Id: Ia2462447f7a0cc2534e877976838de09e8683e89

openstack/i18n,openstack/i18n