Gerrit plugins can contribute to submit rules evaluation, that are a
part of secondary index. Therefore it is crucial that plugins are
loaded prior to triggering of online reindexing.
This change de-couples online reindex activation from index module and
thus postpones the triggering of online reindexing until after loading
of the plugins:
1. Load secondary index
2. Load all plugins
3. Trigger online reindex if needed
Bug: Issue 10082
Change-Id: I1706d42cb50eb342c2b9eca076e2def5bd1426c0
020758e134