torizon: Do not update if Lockbox is available at startup

If Lockbox is available when aktualizr process starts, don't
proceed with an Offline Update. Instead only perform an Offline
Update if Lockbox becomes available while aktualizr is running.

Doing so prevents a possible boot loop that may occur on OS
rollback.

Signed-off-by: Jeremias Cordoba <[email protected]>

include/libaktualizr/aktualizr.h

@@ -413,7 +413,7 @@ class Aktualizr {
     SourceExistsNoContent,
     SourceExists,
   };
-  OffUpdSourceState offupd_source_state_{OffUpdSourceState::SourceDoesNotExist};
+  OffUpdSourceState offupd_source_state_{OffUpdSourceState::Unknown};
 
  protected:
   Aktualizr(Config config, std::shared_ptr<INvStorage> storage_in, const std::shared_ptr<HttpInterface>& http_in);