Add accessor for Repo._initialized
Add accessor for Repo._initialized

I will need later on to verify whether a repository has been
initialized. Using the propery _initialized directly cause some linting
errors, so here is a trivial accessor around it.

Change-Id: I1b03031ff31e68115e9bea4e0bbcadf93772a386

wikimedia/integration-zuul,wikimedia/integration-zuul,gooddata/zuul,gooddata/zuul,wikimedia/integration-zuul,wikimedia/integration-zuul,gooddata/zuul,gooddata/zuul,gooddata/zuul