examples/ubuntu/prerequisites: add APT_GET_OPTS and remove -y

Bug: 23884877
Change-Id: Iaf1c0c47eb95ec4703fe68408d32d7078309c856
Reviewed-on: https://weave-review.googlesource.com/1140
Reviewed-by: Vitaly Buka <vitalybuka@google.com>

libweave/examples/ubuntu/prerequisites.sh

diff --git a/libweave/examples/ubuntu/prerequisites.sh b/libweave/examples/ubuntu/prerequisites.sh
index d4f12a1..f64f06b 100755
--- a/libweave/examples/ubuntu/prerequisites.sh
+++ b/libweave/examples/ubuntu/prerequisites.sh
@@ -6,7 +6,7 @@
 DIR=$(cd -P -- "$(dirname -- "$0")" && pwd -P)
 ROOT_DIR=$(cd -P -- "$(dirname -- "$0")/../.." && pwd -P)
 
-sudo apt-get install -y \
+sudo apt-get install ${APT_GET_OPTS} \
   autoconf \
   automake \
   binutils \