externalize time_period param in query challenge (elastic#68)

README.md

@@ -83,6 +83,12 @@ The table below shows the track parameters that can be adjusted along with defau
 
 This challenge runs mixed Kibana queries against the index created in the **elasticlogs-1bn-load** track. No concurrent indexing is performed.
 
+The table below shows the track parameters that can be adjusted along with default values:
+
+| Parameter | Explanation | Type | Default Value |
+| --------- | ----------- | ---- | ------------- |
+| `query_time_period` | The period to run the parallel query tasks specified in seconds | `int` | `1800` |
+
 ### combined-indexing-and-querying
 
 This challenge assumes that the *elasticlogs-1bn-load* track has been executed as it simulates querying against these indices. It shows how indexing and querying through simulated Kibana dashboards can be combined to provide a more realistic benchmark.

eventdata/challenges/elasticlogs-querying.json

@@ -1,6 +1,8 @@
+{% set p_query_time_period = (query_time_period | default(1800)) %}
+
 {
   "name": "elasticlogs-querying",
-  "description": "This challenge simulates a set of Kibana queries against historical data ({{p_query_index_pattern}} indices) without any indexing taking place for a period of 30 minutes. It assumes one of the challenges creating {{p_query_index_pattern}} indices has been run.",
+  "description": "This challenge simulates a set of Kibana queries against historical data ({{p_query_index_pattern}} indices) without any indexing taking place for a period of {{ p_query_time_period / 60 }} minutes. It assumes one of the challenges creating {{p_query_index_pattern}} indices has been run.",
   "meta": {
     "benchmark_type": "querying",
     "target_kibana_queries_per_minute": 5
@@ -14,7 +16,7 @@
     {
       "parallel": {
         "warmup-time-period": 0,
-        "time-period": 1800,
+        "time-period": {{ p_query_time_period }},
         "clients": 4,
         "tasks": [
           {