challtestsrv.py: change address of target (#6234)

Previously challtestsrv.py (used by chisel.py) assumed challtestsrv runs
on localhost. But we can also reach it on the fixed IP 10.77.77.77, and
this allows running chisel2.py from the host in addition to running it
inside a container.

test/challtestsrv.py

@@ -5,11 +5,11 @@ class ChallTestServer:
     """
     ChallTestServer is a wrapper around pebble-challtestsrv's HTTP management
     API. If the pebble-challtestsrv process you want to interact with is using
-    a -management argument other than the default ('http://localhost:8055') you
+    a -management argument other than the default ('http://10.77.77.77:8055') you
     can instantiate the ChallTestServer using the -management address in use. If
     no custom address is provided the default is assumed.
     """
-    _baseURL = "http://localhost:8055"
+    _baseURL = "http://10.77.77.77:8055"
 
     _paths = {
             "set-ipv4": "/set-default-ipv4",