Adding etcd username on linux:system level

The patch moves creation of etcd username on linux:system to be
created by linux.system state because of the fact that in salt > 2016.11
behavior of gid_from_name parameter has been changed so currently if
gid_from_name = True and the group doesn't exist then etcd.server.service
will fail.

https://docs.saltstack.com/en/2016.3/ref/states/all/salt.states.user.html
https://docs.saltstack.com/en/2017.7/ref/states/all/salt.states.user.html

Change-Id: Iea3f9811b83ec9239ce2c219ff3ad99fd6cf2ac3
Related-PROD: PROD-20579
Related-PROD: PROD-20581
diff --git a/metadata/service/server/cluster.yml b/metadata/service/server/cluster.yml
index e688599..2758b51 100644
--- a/metadata/service/server/cluster.yml
+++ b/metadata/service/server/cluster.yml
@@ -2,6 +2,7 @@
 - etcd
 classes:
 - service.etcd.support
+- service.etcd.linux
 parameters:
   etcd:
     server: