This fix is mostly useful for those developers who want to deploy/test
Gerrit in Tomcat, use the embedded H2 database and have automatic init
on deployment.
The init of a new site on startup (from WebAppInitializer) was failing
when the site was provided via the -Dgerrit.site_path property because
we assumed that the database initialization has to be skipped always
when running in a servlet container. However, this is only true for
the case when using the -Dgerrit.init_path. When Gerrit site is provided
via -Dgerrit.site_path then we have to perform database initialization.
Change-Id: Id577f391cd888bd71ec8502e8ad2f621cbc3fd80
e90d6e81d3