Trying to import a submodule from another module and not a package was raising
AttributeError in importlib when it should be an ImportError.

Found when running importlib against test_runpy.
diff --git a/Lib/importlib/test/import_/test_packages.py b/Lib/importlib/test/import_/test_packages.py
index 1a15ebb..faadc32 100644
--- a/Lib/importlib/test/import_/test_packages.py
+++ b/Lib/importlib/test/import_/test_packages.py
@@ -21,6 +21,12 @@
                 with self.assertRaises(ImportError):
                     import_util.import_('pkg.module')
 
+    def test_module_not_package(self):
+        # Try to import a submodule from a non-package should raise ImportError.
+        assert not hasattr(sys, '__path__')
+        with self.assertRaises(ImportError):
+            import_util.import_('sys.no_submodules_here')
+
 
 def test_main():
     from test.support import run_unittest