Fix diskusage test coverage

nilmdb/utils/diskusage.py

@@ -28,6 +28,6 @@ def du(path):
                 size += du(filepath)
         return size
     except OSError as e:
-        if e.errno != errno.ENOENT: # pragma: no cover
+        if e.errno != errno.ENOENT:
             raise
         return 0

tests/test_misc.py

@@ -93,3 +93,4 @@ class TestMisc(object):
         nilmdb.utils.diskusage.du("/dev")
         with assert_raises(OSError):
             nilmdb.utils.diskusage.du("/dev/null/bogus")
+        nilmdb.utils.diskusage.du("super-bogus-does-not-exist")