Use str(), not unicode() to cast URI for use in psycopg2

Hopefully fixes the new DBManager tests

python/plugins/db_manager/db_plugins/postgis/connector.py

@@ -135,7 +135,7 @@ def __init__(self, uri):
         self._checkRasterColumnsTable()
 
     def _connectionInfo(self):
-        return unicode(self.uri().connectionInfo(True))
+        return str(self.uri().connectionInfo(True))
 
     def _checkSpatial(self):
         """ check whether postgis_version is present in catalog """