Catch NotADirectoryError error

Per the documentation [1]:

  exception NotADirectoryError
    Raised when a directory operation (such as os.listdir()) is
    requested on something which is not a directory. On most POSIX
    platforms, it may also be raised if an operation attempts to open or
    traverse a non-directory file as if it were a directory. Corresponds
    to errno ENOTDIR.

Apparently creating a packaged application can cause this issue. There's
no harm in ignoring it so do just that.

Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
Closes-bug: #1980383
Change-Id: I19b14c7f3b70bee5310cafcaa90fcee9003713c6

stevedore/_cache.py

@@ -56,7 +56,7 @@ def _get_mtime(name):
         s = os.stat(name)
         return s.st_mtime
     except OSError as err:
-        if err.errno != errno.ENOENT:
+        if err.errno not in {errno.ENOENT, errno.ENOTDIR}:
             raise
     return -1.0