Fix device/test_http_client tests (#5309)

* update HTTPClient API usage
skip the second POST as end() has different semantics and nulls the client pointer
use bearssl in ssl tests
add delay in python side when shutting down http web server so MacOS does not complain about address already in use

* fix crash if GET/POST was called after end() without a new begin()
update double POST test to insure no crash if POST called after end()
test now are for both AxTLS and BearSSL

* fix small comment typo

libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp

@@ -1036,7 +1036,7 @@ bool HTTPClient::connect(void)
     }
 
 #ifdef HTTPCLIENT_1_1_COMPATIBLE
-    if(!_client) {
+    if(!_client && _transportTraits) {
         _tcpDeprecated = _transportTraits->create();
         _client = _tcpDeprecated.get();
     }