feat: Detect proxy errors

HTTPS proxy introduces several possible error cases, similar to the actual remote server connection:

* proxy name resolution (DNS) error,
* proxy connection error,
* proxy authentication error.

The proxy authentication error can only be recognized by a string in the underlying OSError: the outer exception is a plain remote server connection error.

Although the proxy is used for HTTPS connection, the actual communication for the proxy itself is HTTP. Thus, specifying a HTTPS protocol for the proxy causes a specific WRONG_VERSION_NUMBER SSL error.

insights/client/connection.py

@@ -572,8 +572,19 @@ def test_connection(self, rc=0):
 
         if isinstance(result, REQUEST_FAILED_EXCEPTIONS):
             root_cause = _exception_root_cause(result)
-            if isinstance(result, requests.exceptions.SSLError):
-                logger.error("    Invalid key or certificate.")
+            if isinstance(result, requests.exceptions.ProxyError):
+                proxy_url = self.proxies[urlparse(url).scheme]
+                if isinstance(root_cause, socket.gaierror):
+                    logger.error("    Could not resolve proxy address %s.", proxy_url)
+                elif "407 Proxy Authentication Required" in str(root_cause):
+                    logger.error("    Invalid proxy credentials %s.", proxy_url)
+                else:
+                    logger.error("    Invalid proxy settings %s.", proxy_url)
+            elif isinstance(result, requests.exceptions.SSLError):
+                if "[SSL: WRONG_VERSION_NUMBER]" in str(root_cause):
+                    logger.error("    Invalid proxy address protocol.")
+                else:
+                    logger.error("    Invalid key or certificate.")
             elif isinstance(result, requests.exceptions.ConnectionError) and isinstance(root_cause, socket.gaierror):
                 self._test_connection(url)
             else: