rework etcd3 install to be like other devstack services

This separates out the install phase early from the start phase to
make this mirror other services in devstack.

Depends-On: I4124dc7e3fd3b4d973979da85209ec991c0f8c4b

Change-Id: I76f8740448b25a48869ee80006e826baa6cafc2b
diff --git a/lib/oslo b/lib/oslo
index d15a303..cbfd5fb 100644
--- a/lib/oslo
+++ b/lib/oslo
@@ -109,7 +109,14 @@
     _do_install_oslo_lib "stevedore"
     _do_install_oslo_lib "taskflow"
     _do_install_oslo_lib "tooz"
+    # installation of additional libraries
+    #
+    # os-traits for nova
     _do_install_oslo_lib "os-traits"
+
+    # etcd (because tooz does not have a hard dependency on these)
+    pip_install etcd3
+    pip_install etcd3gw
 }
 
 # Restore xtrace