Add mailing list for OpenStack SIGs

SIGs are a new construct aimed at replacing dev-centric
and ops-centric workgroups, introduced in [1]. For those
SIGs to have discussions without picking between openstack-dev
and openstack-ops (or worse, cross-posting between those),
create a new common SIG mailing-list (with one topic per SIG).

Yet another mailing-list... Trust me, I hear you... But this
avoids creating one mailing-list per SIG. We should also be
able to discontinue a number of workgroup-specific MLs, as
they migrate to become SIGs. Candidates include interop-wg,
enterprise-wg, product-wg, Openstack-security, OpenStack-HPC...
So this might be a net win !

This is the first step in this transition. Once the list is
set up, we'll prime the pump by creating a "meta" SIG (a SIG
about improving communication between ops and devs in general,
and SIGs in particular), and the meta SIG will then promote
the list and reach out to workgroups to transition them one
by one.

[1]
http://lists.openstack.org/pipermail/openstack-dev/2017-June/118723.html

Change-Id: Icf6b91ac4d65b43cd1ab8c6b41a2a31aa5270066

modules/openstack_project/manifests/lists.pp

@@ -278,6 +278,15 @@ class openstack_project::lists(
     mailserver  => $listdomain,
   }
 
+  maillist { 'openstack-sigs':
+    ensure      => present,
+    admin       => 'thierry@openstack.org',
+    password    => $listpassword,
+    description => 'OpenStack SIGs discussions, gathering users, operators and developers of OpenStack into common groups.',
+    webserver   => $listdomain,
+    mailserver  => $listdomain,
+  }
+
   maillist { 'enterprise-wg':
     ensure      => present,
     admin       => 'carol.l.barrett@intel.com',