metrics: Add metrics user and group

BUG=None
TEST=With chromium:1691167, perform emerge-${BOARD} metrics,
then check /build/<board>/etc/passwd, see user and group metrics

Change-Id: Ie27310f5fd82b588348318dadcbd4ba783e47608
Reviewed-on: https://chromium-review.googlesource.com/1691167
Tested-by: Hardik Goyal <hardikgoyal@google.com>
Commit-Ready: Hardik Goyal <hardikgoyal@google.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
diff --git a/profiles/base/accounts/group/metrics b/profiles/base/accounts/group/metrics
new file mode 100644
index 0000000..5c3131e
--- /dev/null
+++ b/profiles/base/accounts/group/metrics
@@ -0,0 +1,3 @@
+group:metrics
+gid:20140
+users:metrics
diff --git a/profiles/base/accounts/user/metrics b/profiles/base/accounts/user/metrics
new file mode 100644
index 0000000..57215aa
--- /dev/null
+++ b/profiles/base/accounts/user/metrics
@@ -0,0 +1,6 @@
+user:metrics
+uid:20140
+gid:20140
+gecos:user for metrics_daemon to run its services in sandboxed environment
+home:/dev/null
+shell:/bin/false