Undefined names may raise NameError at runtime

[cclauss]

flake8 testing of https://github.com/CellProfiler/python-bioformats on Python 3.7.0

$ flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics

./bioformats/omexml.py:1164:39: F821 undefined name 'NS_SPW'
            make_text_node(self.node, NS_SPW, "Description", test)
                                      ^
./bioformats/omexml.py:1164:62: F821 undefined name 'test'
            make_text_node(self.node, NS_SPW, "Description", test)
                                                             ^
./bioformats/__init__.py:98:5: F821 undefined name 'J'
    J.kill_vm()
    ^
./bioformats/formatreader.py:751:59: F821 undefined name 'path'
                    "The file, \"%s\", does not exist." % path
                                                          ^
./bioformats/formatreader.py:752:21: F821 undefined name 'path'
                    path)
                    ^
5     F821 undefined name 'J'
5