Testing port server

run_tests.py will start a server (if it's not running, or if the running
port server mismatches the 'current' one) that serves ports to use for
tests. The server is left running after run_tests.py finishes, so that
in environments such as Mac and Windows where tests run unshielded from
each other, we don't start jumping on already used ports.
diff --git a/src/core/security/credentials.c b/src/core/security/credentials.c
index 15268ce..c45b5c0 100644
--- a/src/core/security/credentials.c
+++ b/src/core/security/credentials.c
@@ -679,7 +679,7 @@
   request.path = GRPC_GOOGLE_OAUTH2_SERVICE_TOKEN_PATH;
   request.hdr_count = 1;
   request.hdrs = &header;
-  request.use_ssl = 1;
+  request.handshaker = &grpc_httpcli_ssl;
   grpc_httpcli_post(httpcli_context, pollset, &request, body, strlen(body),
                     deadline, response_cb, metadata_req);
   gpr_free(body);
@@ -738,7 +738,7 @@
   request.path = GRPC_GOOGLE_OAUTH2_SERVICE_TOKEN_PATH;
   request.hdr_count = 1;
   request.hdrs = &header;
-  request.use_ssl = 1;
+  request.handshaker = &grpc_httpcli_ssl;
   grpc_httpcli_post(httpcli_context, pollset, &request, body, strlen(body),
                     deadline, response_cb, metadata_req);
   gpr_free(body);