storage+bundle: Clean old bundle data before new activation (#4944)

If OPA has an activated bundle that owns all roots
and a new bundle with empty roots is to be activated, the
old bundle's data should first be erased from the store.
Currently both the old and new data is kept in the store.

This commit attempts to fix this by providing an indication to
the truncate call about the scenario in which the root is to be
overwritten.

Fixes: #4940

Signed-off-by: Ashutosh Narkar <anarkar4387@gmail.com>

bundle/store.go

@@ -727,6 +727,16 @@ func writeDataAndModules(ctx context.Context, store storage.Store, txn storage.T
 				}
 			}
 		} else {
+			var rootOverwrite bool
+			for _, root := range *b.Manifest.Roots {
+				if root == "" {
+					rootOverwrite = true
+					break
+				}
+			}
+
+			params.RootOverwrite = rootOverwrite
+
 			err := store.Truncate(ctx, txn, params, NewIterator(b.Raw))
 			if err != nil {
 				return fmt.Errorf("store truncate failed for bundle '%s': %v", name, err)