Install: Validate database before migrating (#12867)

* Validate database during install
Needed to remove usages of legacy functions in the validation

* Fix output, restore real versions

LibreNMS/DB/Schema.php

@@ -28,6 +28,7 @@ use DB;
 use Illuminate\Support\Str;
 use LibreNMS\Config;
 use LibreNMS\Util\Version;
+use PDOException;
 use Schema as LaravelSchema;
 use Symfony\Component\Yaml\Yaml;
 
@@ -111,6 +112,25 @@ class Schema
         return $this->schema;
     }
 
+    /**
+     * Get the schema version from the previous schema system
+     */
+    public static function getLegacySchema(): int
+    {
+        try {
+            $db = \LibreNMS\DB\Eloquent::DB();
+            if ($db) {
+                return (int) $db->table('dbSchema')
+                    ->orderBy('version', 'DESC')
+                    ->value('version');
+            }
+        } catch (PDOException $e) {
+            // return default
+        }
+
+        return 0;
+    }
+
     /**
      * Get a list of all tables.
      *