Update docker image tag for gainsight

Since gainsight has new tag - 2019.2.3 - for new release,
its required to set it explicit for this specific release.

Change-Id: Id2451d548dd5035baaa83fe86c30e8072e92fccc
Related-Bug: PROD-27752
diff --git a/defaults/docker_images.yml b/defaults/docker_images.yml
index 35c44a9..6adab6b 100644
--- a/defaults/docker_images.yml
+++ b/defaults/docker_images.yml
@@ -29,7 +29,7 @@
     docker_image_grafana: "${_param:mcp_docker_registry}/openstack-docker/grafana:${_param:mcp_version}"
     docker_image_prometheus_es_exporter: "${_param:mcp_docker_registry}/mirantis/external/braedon/prometheus-es-exporter:0.5.1"
     docker_image_prometheus: "${_param:mcp_docker_registry}/openstack-docker/prometheus:${_param:mcp_version}"
-    docker_image_prometheus_gainsight: "${_param:mcp_docker_registry}/openstack-docker/gainsight:${_param:mcp_version}"
+    docker_image_prometheus_gainsight: "${_param:mcp_docker_registry}/openstack-docker/gainsight:2019.2.3"
     docker_image_prometheus_gainsight_elasticsearch: "${_param:mcp_docker_registry}/openstack-docker/gainsight_elasticsearch:${_param:mcp_version}"
     docker_image_prometheus_relay: "${_param:mcp_docker_registry}/openstack-docker/prometheus_relay:${_param:mcp_version}"
     docker_image_pushgateway: "${_param:mcp_docker_registry}/openstack-docker/pushgateway:${_param:mcp_version}"