Provide ability to configure keystone resync interval

Contrail API provides an option 'keystone_resync_interval_secs'.
Its default value of 60sec is not always convenient.
This commit introduces support of this param in formula.

Change-Id: I43bff19d4120fe86759efb56f28afc64e44e2d91
Related-PROD: PROD-27794
(cherry picked from commit 94eba6c8d1ba8fddafc0d16ef3f4247ac4dc93f8)
diff --git a/README.rst b/README.rst
index 829e827..501f90c 100644
--- a/README.rst
+++ b/README.rst
@@ -897,6 +897,17 @@
           sync_on_demand: false
       ...
 
+Configure duration between polls to keystone to sync domains and projects
+-------------------------------------------------------------------------
+
+.. code-block:: yaml
+
+    opencontrail:
+      ...
+      config:
+        keystone_resync_interval_secs: 60
+      ...
+
 Cassandra listen configuration
 ------------------------------
 
diff --git a/opencontrail/files/4.0/contrail-api.conf b/opencontrail/files/4.0/contrail-api.conf
index 975b093..62645d8 100644
--- a/opencontrail/files/4.0/contrail-api.conf
+++ b/opencontrail/files/4.0/contrail-api.conf
@@ -52,6 +52,9 @@
 {%- elif config.get('sandesh_send_rate_limits', {}).get('global') %}
 sandesh_send_rate_limit={{ config.sandesh_send_rate_limits.global }}
 {%- endif %}
+{%- if config.keystone_resync_interval_secs is defined %}
+keystone_resync_interval_secs={{ config.keystone_resync_interval_secs }}
+{%- endif %}
 
 # (StrOpt) default encoding to use for string resources.
 # this is optional variable. Define it if you want to override