shill: vpn: Add vpn user and group

VPN clients in shill will be run as vpn:vpn. Also add shill to the vpn
group and thus shill could modify the config files that will be read by
clients.

This user is going to replace "openvpn" and "ipsec" users for running
the corresponding clients.

BUG=b:177984585
TEST=None

Cq-Depend: chromium:2717251
Change-Id: I1893b5aca043400c8d20ca1060e86d68abb3bdd2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/eclass-overlay/+/2699947
Tested-by: Jie Jiang <jiejiang@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Hugo Benichi <hugobenichi@google.com>
Commit-Queue: Jie Jiang <jiejiang@chromium.org>
diff --git a/profiles/base/accounts/group/vpn b/profiles/base/accounts/group/vpn
new file mode 100644
index 0000000..1bfc2c2
--- /dev/null
+++ b/profiles/base/accounts/group/vpn
@@ -0,0 +1,5 @@
+# Members of this group have access to the files used by VPN clients
+# (e.g., configuration files)
+group:vpn
+gid:20174
+users:vpn,shill
diff --git a/profiles/base/accounts/user/vpn b/profiles/base/accounts/user/vpn
new file mode 100644
index 0000000..2236ba3
--- /dev/null
+++ b/profiles/base/accounts/user/vpn
@@ -0,0 +1,6 @@
+user:vpn
+uid:20174
+gid:20174
+gecos:CrOS VPN clients
+home:/dev/null
+shell:/bin/false