Undefined name: Add missing "value" parameter to a setter

[cclauss]

flake8 testing of https://github.com/codait/graph_def_editor on Python 3.7.1

$ flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics

./graph_def_editor/node.py:358:14: F821 undefined name 'value'
    for s in value:
             ^
./graph_def_editor/node.py:362:31: F821 undefined name 'value'
    self._colocation_groups = value
                              ^
2    F821 undefined name 'value'
2

E901,E999,F821,F822,F823 are the "showstopper" flake8 issues that can halt the runtime with a SyntaxError, NameError, etc. These 5 are different from most other flake8 issues which are merely "style violations" -- useful for readability but they do not effect runtime safety.

• F821: undefined name name
• F822: undefined name name in __all__
• F823: local variable name referenced before assignment
• E901: SyntaxError or IndentationError
• E999: SyntaxError -- failed to compile a file into an Abstract Syntax Tree