Move initialization of context to thread local object

[spilchen]

The context global variable was already thread local, but its
initialization was only being triggered during the initial import of the
package. Moved all of the setup of the context variable to a init
function of a class that inherits from threading.local. This ensures
that when a thread starts it will run the init function.

This avoids errors like the following:

Traceback (most recent call last):
  File "src/gevent/greenlet.py", line 854, in gevent._gevent_cgreenlet.Greenlet.run
  File "/root/src/es-cp4d-locust/env/lib/python3.6/site-packages/locust/user/users.py", line 161, in run_user
    user.run()
  File "/root/src/es-cp4d-locust/env/lib/python3.6/site-packages/locust/user/users.py", line 128, in run
    self.on_start()
  File "/root/src/es-cp4d-locust/locustfile.py", line 58, in on_start
    CFG['oc']['namespace'])
  File "/root/src/py-es-cp4d/db2_eventstore_cp4d/context.py", line 23, in __init__
    oc.login(username, password)
  File "/root/src/openshift-client-python/packages/openshift/base_verbs.py", line 156, in login
    r.add_action(oc_action(cur_context(), "login", cmd_args=['-u', username, '-p', password, cmd_args]))
  File "/root/src/openshift-client-python/packages/openshift/context.py", line 37, in cur_context
    return context.stack[-1]
  File "src/gevent/local.py", line 408, in gevent._gevent_clocal.local.__getattribute__
AttributeError: 'gevent._gevent_clocal.local' object has no attribute 'stack'

[bradmwilliams]

@spilchen In order for you changes to pass the pr-merge check, you'll need to address this error:
You need to run ansible/rebuild_module.sh and include changes in this PR

[spilchen]

Thanks, I ran the script.