[show][config][plugin] add processing of ModuleNotFoundError with warning log message instead of default error message

Avoid excess error messages for cases of race conditions when plugin was
removed right before the stage of its loading

Signed-off-by: Maksym Kovalchuk <mkovalchuk@nvidia.com>

Author: maksym-kovalchuk

utilities_common/util_base.py

@@ -29,6 +29,12 @@ def iter_namespace(ns_pkg):
             log.log_debug('importing plugin: {}'.format(module_name))
             try:
                 module = importlib.import_module(module_name)
+
+            except ModuleNotFoundError as err:
+                log.log_warning('failed to import plugin {}: {}'.format(module_name, err),
+                              also_print_to_console=True)
+                continue
+
             except Exception as err:
                 log.log_error('failed to import plugin {}: {}'.format(module_name, err),
                               also_print_to_console=True)