Error 502

[jbrunetext]

**Output of the info page **

(paste your output here)

Additional environment details (Operating System, Cloud provider, etc):

Steps to reproduce the issue:
1.use any version of Datadog
2.use proxy web zscaler : port 80
3.user agent Docker with rancher server 1.6.18

Describe the results you received:
UTC | ERROR | dd.forwarder | forwarder(ddagent.py:282) | Response: HTTPResponse(_body=None,buffer=None,code=599,effective_url='https://intake/?api_key=*************************db7fb',error=CurlError('HTTP 599: Received HTTP code 502 from proxy after CONNECT',),headers={},reason='Unknown',request=<tornado.httpclient.HTTPRequest object at 0x7f68dc4aa9d0>,request_time=0.026569843292236328,time_info={})
2018-08-23 13:29:03 UTC | WARNING | dd.forwarder | transaction(transaction.py:268) | Transaction 40 in error (4 errors), it will be replayed after 2018-08-23 13:30:23
2018-08-23 13:29:07 UTC | ERROR | dd.forwarder | forwarder(ddagent.py:282) | Response: HTTPResponse(_body=None,buffer=None,code=599,effective_url='https://api/v1/series/?api_key=*************************db7fb',error=CurlError('HTTP 599: Received HTTP code 502 from proxy after CONNECT',),headers={},reason='Unknown',request=<tornado.httpclient.HTTPRequest object at 0x7f68dc4aa9d0>,request_time=0.031332969665527344,time_info={})
2018-08-23 13:29:07 UTC | WARNING | dd.forwarder | transaction(transaction.py:268) | Transaction 68 in error (3 errors), it will be replayed after 2018-08-23 13:30:07
2018-08-23 13:29:07 UTC | ERROR | dd.forwarder | forwarder(ddagent.py:282) | Response: HTTPResponse(_body=None,buffer=None,code=599,effective_url='https://api/v1/check_run/?api_key=*************************db7fb',error=CurlError('HTTP 599: Received HTTP code 502 from proxy after CONNECT',),headers={},reason='Unknown',request=<tornado.httpclient.HTTPRequest object at 0x7f68ddf4ed90>,request_time=0.026308059692382812,time_info={})
2018-08-23 13:29:07 UTC | WARNING | dd.forwarder | transaction(transaction.py:268) | Transaction 66 in error (3 errors), it will be replayed after 2018-08-23 13:30:07
2018-08-23 13:29:08 UTC | ERROR | dd.forwarder | forwarder(ddagent.py:282) | Response: HTTPResponse(_body=None,buffer=None,code=599,effective_url='https://api/v1/series/?api_key=*************************db7fb',error=CurlError('HTTP 599: Received HTTP code 502 from proxy after CONNECT',),headers={},reason='Unknown',request=<tornado.httpclient.HTTPRequest object at 0x7f68dc4aa9d0>,request_time=0.016031980514526367,time_info={})
2018-08-23 13:29:08 UTC | WARNING | dd.forwarder | transaction(transaction.py:268) | Transaction 31 in error (3 errors), it will be replayed after 2018-08-23 13:30:08
2018-08-23 13:29:08 UTC | ERROR | dd.forwarder | forwarder(ddagent.py:282) | Response: HTTPResponse(_body=None,buffer=None,code=599,effective_url='https://intake/?api_key=*************************db7fb',error=CurlError('HTTP 599: Received HTTP code 502 from proxy after CONNECT',),headers={},reason='Unknown',request=<tornado.httpclient.HTTPRequest object at 0x7f68dc4aa9d0>,request_time=0.016971826553344727,time_info={})

Describe the results you expected:
Code 200

Additional information you deem important (e.g. issue happens only occasionally):