Do not serialize the 'base' role

The base role needs the 'peer_ip' host var from other hosts, so
we have to run the fact discovery step on all hosts before starting
to execute tasks.

site.yml

@@ -3,10 +3,6 @@
 - hosts: all
   roles:
     - base
-  serial:
-    - 1
-    - 1
-    - "100%"
 
 - hosts: etcd
   roles: