VCA start_build changed to make it non-interactive

Change-Id: Ie74b821cc358a100a04e20e4f0e2373e7dc74e6f
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>

jenkins/VCA/start_build

@@ -48,7 +48,7 @@ EOF
 systemctl enable lxd-bridge
 systemctl start lxd-bridge
 lxc image copy ubuntu:16.04 local: --alias ubuntu-xenial
-add-apt-repository ppa:juju/devel
+add-apt-repository -y ppa:juju/devel
 apt update
 apt install -y juju
 juju bootstrap juju localhost