Past.traslate module assumes tmp folder to be present, even on windows platform

[kapilkd13]

I am working on a project that uses past module to run some python 2 code on python3 on Windows OS.
Here is the error:

PS C:\> cwltool
Traceback (most recent call last):
  File "C:\Program Files (x86)\Python\Python3.6\Scripts\cwltool-script.py", line 11, in <module>
    load_entry_point('cwltool==1.0.20170723124118', 'console_scripts', 'cwltool')()
  File "c:\program files (x86)\python\python3.6\lib\site-packages\pkg_resources\__init__.py", line 565, in load_entry_point
    return get_distribution(dist).load_entry_point(group, name)
  File "c:\program files (x86)\python\python3.6\lib\site-packages\pkg_resources\__init__.py", line 2631, in load_entry_point
    return ep.load()
  File "c:\program files (x86)\python\python3.6\lib\site-packages\pkg_resources\__init__.py", line 2291, in load
    return self.resolve()
  File "c:\program files (x86)\python\python3.6\lib\site-packages\pkg_resources\__init__.py", line 2297, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "c:\program files (x86)\python\python3.6\lib\site-packages\cwltool\main.py", line 22, in <module>
    import schema_salad.validate as validate
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load
  File "<frozen importlib._bootstrap>", line 950, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 646, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 616, in _load_backward_compatible
  File "c:\program files (x86)\python\python3.6\lib\site-packages\past\translation\__init__.py", line 341, in load_module
    mod = imp.load_module(fullname, *self.found)
  File "c:\program files (x86)\python\python3.6\lib\imp.py", line 234, in load_module
    return load_source(name, filename, file)
  File "c:\program files (x86)\python\python3.6\lib\imp.py", line 172, in load_source
    module = _load(spec)
  File "c:\program files (x86)\python\python3.6\lib\site-packages\schema_salad\validate.py", line 3, in <module>
    import avro.schema
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load
  File "<frozen importlib._bootstrap>", line 950, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 646, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 616, in _load_backward_compatible
  File "c:\program files (x86)\python\python3.6\lib\site-packages\past\translation\__init__.py", line 396, in load_module
    if detect_python2(source, self.pathname):
  File "c:\program files (x86)\python\python3.6\lib\site-packages\past\translation\__init__.py", line 222, in detect_python2
    with open('/tmp/original_code.py', 'w') as f:
FileNotFoundError: [Errno 2] No such file or directory: '/tmp/original_code.py'

This problem arises because of the hardcoded tmp folder while writing the to a file in past module see here https://github.com/PythonCharmers/python-future/blob/master/src/past/translation/__init__.py#L221

We should remove this hardcoding and use tmp env variable.