[db_manager] Fix postgis plugins loading

Fix infinite recursion on load calls

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

@@ -21,17 +21,19 @@
 """
 
 import os
+from importlib import import_module
 
 current_dir = os.path.dirname(__file__)
 
 
-def load(dbplugin, mainwindow):
+def load(db, mainwindow):
     for name in os.listdir(current_dir):
         if not os.path.isdir(os.path.join(current_dir, name)):
             continue
+        if name in ('__pycache__'):
+            continue
         try:
-            exec(u"from .%s import load" % name)
+            plugin_module = import_module('.'.join((__package__, name)))
         except ImportError:
             continue
-
-        load(dbplugin, mainwindow)
+        plugin_module.load(db, mainwindow)