Kill create_cluster pillar switch, refs: #100

It is just a variant of init_db. A more correct solution would be to
support configuring a different initdb command while passing values from
the pillar by default like version. This would make it truly generic but
is probably not achievable given current pillar self-referencing
capabilities (ie. none).

Thus, I decided to make it OS family specific since Debian provides its
own tools to manage clusters, etc. Gentoo also has a specific way to
initialize a new cluster which does not fit with commands.initdb so
the current if/elif would be extended when support is added for Gentoo.

postgres/defaults.yaml

@@ -8,8 +8,6 @@ postgres:
   service: postgresql
   conf_dir: /var/lib/pgsql/data
   data_dir: /var/lib/pgsql/data
-  create_cluster: False
-  init_db: False
   version: 9.1
   use_upstream_repo: False
   users: {}
@@ -19,9 +17,10 @@ postgres:
   postgresconf_backup: True
   postgresconf: ""
   pg_hba.conf: salt://postgres/pg_hba.conf
-  commands:
-    initdb: service postgresql initdb
+  initdb: True
   initdb_user: root
   initdb_args: --data-checksum
+  commands:
+    initdb: service postgresql initdb
   user: postgres
   group: postgres