Add option to make cache expiration configurable

This commit adds a cache_expiration parameter to make the cache
expiration for the api configurable. By default it sets it 15min
(which is half of the far more conservative openstack-health default)
to match the longest e-r query times seen in testing.

Change-Id: Iaea17e16f6995121ad54bae2c46a96112b702caf

manifests/api.pp

@@ -18,6 +18,7 @@ class openstack_health::api(
   $elastic_recheck_dir = '/opt/elastic-recheck',
   $elastic_recheck_repo = 'https://git.openstack.org/openstack-infra/elastic-recheck',
   $elastic_recheck_revision = 'master',
+  $cache_expiration = 900,
 ) {
 
   include ::httpd::mod::wsgi

templates/openstack-health.conf.erb

@@ -1,5 +1,6 @@
 [default]
 query_dir = <%= @elastic_recheck_dir %>/queries
+cache_expiration = <%= @cache_expiration %>
 db_uri = <%= scope.lookupvar("openstack_health::api::db_uri") %>
 <% if @ignored_keys.length > 0 -%>
 ignored_run_metadata_keys =