Avoid SiteSQLStore::newInstance and the deprecated Sites class

Due to the fact that the SiteStore which is used by most of the
production code is being cached now, just using TestSites::insertIntoDb
wont work anymore as that doesn't affect the cache of the other
SiteStore instances.

Bug: 64743
Change-Id: Ifed24937ee5af3cc723451621ddfc6a272b737df
Merge "Avoid SiteSQLStore::newInstance and the deprecated Sites class"