The forced reindex is not needed when the project index is present.
Preserve the automatic reindex of projects for new sites and defer
to reindex site program or online reindexing if project index already
exists.
The check is implemented in index backend agnostic manner, so that it
should work for both supported backends: Lucene and Elasticsearch. It
should also work independently whether or not a project index schema
migration is needed during upgrade.
Reindexing projects is a very expensive operation and can turn a simple
upgrade to a long and painful operation because of the increase of the
migration time and the amount of memory needed.
Bug: Issue 12680
Change-Id: I3a4f1d07405f7bb631467d1f005d48cb56ee867f
bb0b777254