MISP: fix requirements; enum not required for python 3.4+

[rolinh]

Request Type

Bug

Work Environment

Question	Answer
OS version (server)	N/A
OS version (client)	N/A
Cortex Analyzer Name	MISP
Cortex Analyzer Version	1.15.1
Cortex Version	N/A
Browser type & version	N/A

Description

PR #398 may fix an issue with Ubuntu 16.04 but it introduces another: enum is apparently in python standard library since v3.4 (check this link).

The added dependency causes issues when using (at least) python 3.6:

/opt/analyzers/MISP # pip3 install -r requirements.txt
Ignoring future: markers 'python_version <= "2.7"' don't match your environment
Requirement already satisfied: cortexutils in /usr/lib/python3.6/site-packages (from -r requirements.txt (line 1)) (1.3.0)
Collecting pymisp (from -r requirements.txt (line 2))
  Using cached https://files.pythonhosted.org/packages/2d/69/0b24012a55d21b174df044abed612669c30615cde559f9389a22df9c3062/pymisp-2.4.99-py3-none-any.whl
Collecting enum (from -r requirements.txt (line 3))
  Using cached https://files.pythonhosted.org/packages/02/a0/32e1d5a21b703f600183e205aafc6773577e16429af5ad3c3f9b956b07ca/enum-0.4.7.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/usr/lib/python3.6/site-packages/setuptools/__init__.py", line 6, in <module>
        import distutils.core
      File "/usr/lib/python3.6/distutils/core.py", line 16, in <module>
        from distutils.dist import Distribution
      File "/usr/lib/python3.6/distutils/dist.py", line 9, in <module>
        import re
      File "/usr/lib/python3.6/re.py", line 142, in <module>
        class RegexFlag(enum.IntFlag):
    AttributeError: module 'enum' has no attribute 'IntFlag'

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-install-ljoxw_cm/enum/

Steps to Reproduce

Attempt to pip3 install -r requirements.txt for the MISP analyzer with Python 3.6.

Possible Solutions

My guess is that the enum package is only required for python < 3.4. Thus, the requirements.txt file can probably be modified for something like:

cortexutils
pymisp
enum;python_version<'3.4'
future;python_version<='2.7'

At the very least, I can confirm that enum is not required with python 3.6.

[3c7]

Thanks for reporting!