Cold boot handling

[kjac]

Indexes must be rebuilt when a cold boot is detected.

Indexes should be rebuilt from the index data stored in the DB, so that needs to be in place before this task can be started.

NOTE: This might search technology dependent. Cold boots may have to be handled differently for in-process engines vs. out-of-process ones. Or, in other words, we do not want to end up in a scenario, where out-of-process indexes are rebuilt, just because an instance was shifted in Azure.