Set workers=$API_WORKERS in glance-registry.conf

We use $API_WORKERS to throttle the number of workers
in other services but were not doing it for g-reg for
some reason, which by default will run ncpu workers
up to a limit of 8.

Change-Id: Idc81ce05546e6d625c10e2229256eafbe7c057a5
Closes-Bug: #1774781
diff --git a/lib/glance b/lib/glance
index 6a0e719..528a05f 100644
--- a/lib/glance
+++ b/lib/glance
@@ -114,6 +114,7 @@
     # Set non-default configuration options for registry
     iniset $GLANCE_REGISTRY_CONF DEFAULT debug $ENABLE_DEBUG_LOG_LEVEL
     iniset $GLANCE_REGISTRY_CONF DEFAULT bind_host $GLANCE_SERVICE_LISTEN_ADDRESS
+    iniset $GLANCE_REGISTRY_CONF DEFAULT workers $API_WORKERS
     local dburl
     dburl=`database_connection_url glance`
     iniset $GLANCE_REGISTRY_CONF database connection $dburl