[skolo] Add shelf3 RPis to hosts.ini.

In preparation for bringing up shelf3.

Change-Id: I18b1b2ecbc11c332bf9a60aa481fe21bf1656478
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/435621
Reviewed-by: Kevin Lubick <kjlubick@google.com>
diff --git a/skolo/ansible/hosts.ini b/skolo/ansible/hosts.ini
index 6759d45..bdc2bf1 100644
--- a/skolo/ansible/hosts.ini
+++ b/skolo/ansible/hosts.ini
@@ -27,8 +27,10 @@
 rack3_linux
 rack5_linux
 
+# Temporary group until all RPis are on Switchboard.
 [switchboard_rpis]
 skia-rpi2-rack4-shelf1-[001:008]
+skia-rpi2-rack4-shelf3-[001:016]
 
 [rpis:children]
 rack4_rpis
@@ -38,6 +40,7 @@
 [rack4_rpis:children]
 rack4_shelf1
 rack4_shelf2
+rack4_shelf3
 
 [rack4_shelf1]
 skia-rpi2-rack4-shelf1-[001:020]
@@ -46,6 +49,10 @@
 [rack4_shelf2]
 skia-rpi2-rack4-shelf2-[001:024]
 
+[rack4_shelf3]
+skia-rpi2-rack4-shelf3-[001:016]
+
+
 # A small subset of rack1 used to pre-trial actions.
 [rack1_rpis_incremental_rollout]
 skia-rpi-001