Update configuration.py

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PRs will read environment variables assigned for proxy and no_proxy.

Author: p172913

kubernetes/client/configuration.py

@@ -158,9 +158,15 @@ def __init__(self, host="http://localhost",
         """
 
         self.proxy = None
+        if(os.getenv("HTTPS_PROXY")):self.proxy=os.getenv("HTTPS_PROXY")
+        if(os.getenv("https_proxy")):self.proxy=os.getenv("https_proxy")
+        if(os.getenv("HTTP_PROXY")):self.proxy=os.getenv("HTTP_PROXY")
+        if(os.getenv("http_proxy")):self.proxy=os.getenv("http_proxy")
         """Proxy URL
         """
         self.no_proxy = None
+        if(os.getenv("NO_PROXY")):self.no_proxy=os.getenv("NO_PROXY")
+        if(os.getenv("no_proxy")):self.no_proxy=os.getenv("no_proxy")
         """bypass proxy for host in the no_proxy list.
         """
         self.proxy_headers = None