Implement acceptance test for dynamic configuration functionality

and fix some bugs revealed by acceptance tests

features/steps/basic_replication.py

@@ -1,4 +1,6 @@
+import json
 import psycopg2 as pg
+import requests
 
 from behave import step, then
 from time import sleep, time
@@ -52,3 +54,31 @@ def replication_works(context, master, replica, time_limit):
         When I add the table test_{0} to {1}
         Then table test_{0} is present on {2} after {3} seconds
     """.format(int(time()), master, replica, time_limit))
+
+
+def patch_config_with_data(config, data):
+    for name, value in data.items():
+        if isinstance(value, dict):
+            patch_config_with_data(config[name], value)
+        else:
+            config[name] = value
+
+
+@step('I patch global configuration with {data}')
+def patch_config(context, data):
+    data = json.loads(data)
+    config = json.loads(context.dcs_ctl.query('config'))
+    patch_config_with_data(config, data)
+    context.dcs_ctl.set('config', json.dumps(config))
+
+
+@then('Response on GET {url} contains {value} after {timeout:d} seconds')
+def check_http_response(context, url, value, timeout):
+    for _ in range(int(timeout)):
+        r = requests.get(url)
+        if value in r.content.decode('utf-8'):
+            break
+        sleep(1)
+    else:
+        assert False,\
+            "Value {0} is not present in response after {1} seconds".format(value, timeout)