caddy-frontend: Improve header management in test backend

Accessing headers.dict results with dropping headers sent in more then one
line, which is accepted by RFC.

So in case if many lines for given header arrived, expose them as a list,
otherwise simply show exactly arrived header.

software/caddy-frontend/test/test.py

@@ -572,9 +572,18 @@ class TestHandler(BaseHTTPRequestHandler):
           header_dict[header] = value.strip()
     if response is None:
       if 'x-reply-body' not in self.headers.dict:
+        headers_dict = dict()
+        for header in self.headers.keys():
+          content = self.headers.getheaders(header)
+          if len(content) == 0:
+            headers_dict[header] = None
+          elif len(content) == 1:
+            headers_dict[header] = content[0]
+          else:
+            headers_dict[header] = content
         response = {
           'Path': self.path,
-          'Incoming Headers': self.headers.dict
+          'Incoming Headers': headers_dict
         }
         response = json.dumps(response, indent=2)
       else: