Fix sphynx error about tornado.version_info
Fix sphynx error about tornado.version_info

This is fix errors like the following when building docs:

WARNING: autodoc: failed to import module 'salt.states.saltmod'; the following exception was raised:
Traceback (most recent call last):
  File "/public/src/salt/env/lib/python3.6/site-packages/sphinx/ext/autodoc/importer.py", line 140, in import_module
    __import__(modname)
  File "/public/src/salt/salt/states/saltmod.py", line 36, in <module>
    import salt.output
  File "/public/src/salt/salt/output/__init__.py", line 19, in <module>
    import salt.loader
  File "/public/src/salt/salt/loader.py", line 23, in <module>
    import salt.config
  File "/public/src/salt/salt/config/__init__.py", line 27, in <module>
    import salt.utils.network
  File "/public/src/salt/salt/utils/network.py", line 35, in <module>
    import salt.utils.zeromq
  File "/public/src/salt/salt/utils/zeromq.py", line 39, in <module>
    if tornado.version_info < (5,):
TypeError: '<' not supported between instances of 'Mock' and 'tuple'

(cherry picked from commit 8199700fdb786cd1713e211e1ffbbdc1c36fc869)

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt