Current CI Broken at docker_metric.

[rkooo567]

Current CI has been broken at docker_metric integration test due to the error,

[integration_py3_docker_metric] 19-04-29:10:25:29 ERROR [clipper_metric_docker.py:127] Failed to parse: http://localhost:23298/api/v1/series?match[]=clipper_mc_recv_time_ms_sum

I found out urllib3 recently released their new version 1.25 on April 22nd (which is the day our CI starts to be broken).

Our requests library uses urllib3 as its dependency. I strongly suspect the version of urllib3 is the cause of our broken CI. I also found this issue from requests library. It says there's an issue with urllib3 1.25. (It is not directly related to our issue btw).
https://github.com/kennethreitz/requests/issues/5067

Here is also the logs that I found from our Jenkins

[integration_py3_docker_metric] /usr/local/lib/python3.5/dist-packages/requests/__init__.py:91: RequestsDependencyWarning: urllib3 (1.25.1) or chardet (3.0.4) doesn't match a supported version!

[integration_py3_docker_metric] RequestsDependencyWarning)

As you can see, we are currently using urllib3 1.25.1. I will create a PR to restrict the urllib3's version to be less than 1.25 and see if it resolves our problem.

-> I verified the problem is because urllib3 version is set to be 1.25.1. In local vm environment, it was broken if I use 1.25.1. We should use either 1.25.2 or <1.25

[rkooo567]

It is merged and resolved. I will keep opening the issue so that we can remove urllib3 version constraint later once it becomes stabilized

[rkooo567]

https://github.com/kennethreitz/requests/pull/5092 says request library is now compatible to urllib 1.25.2. But it is still not compatible to 1.25.1 or 1.25. I will just keep them as is because using 1.25.2 wouldn't make any difference.