Fix CNI_COMMAND=VERSION case

In case of VERSION command k8s v1.16 and higher sends
only {"cniVersion": "0.4.0"} to the stdio, but kuryr-cni
expected cni-conf with kuryr_conf field.

Also k8s expects json in the stdio, but logs was also there.
So need to strictly redirect it into stderr in this case.

It's a work around, because maintanable way here is to use
golang's version based on containernetworking library.

Change-Id: I9095ced11f78eb1ae2890883fa6da4df74213480
Signed-off-by: Alexey Perevalov <a.perevalov@samsung.com>

kuryr_kubernetes/cni/main.py

@@ -40,7 +40,8 @@ def run():
     else:
         d = jsonutils.load(sys.stdin)
     cni_conf = utils.CNIConfig(d)
-    args = ['--config-file', cni_conf.kuryr_conf]
+    args = (['--config-file', cni_conf.kuryr_conf] if 'kuryr_conf' in d
+            else [])
 
     try:
         if cni_conf.debug:

kuryr_kubernetes/config.py

@@ -329,6 +329,8 @@ logging.register_options(CONF)
 def init(args, **kwargs):
     version_k8s = version.version_info.version_string()
     CONF(args=args, project='kuryr-k8s', version=version_k8s, **kwargs)
+    if os.environ.get('CNI_COMMAND') == 'VERSION':
+        CONF.set_default('use_stderr', True)
 
 
 def setup_logging():