abi/bootstrap: install system dependencies without confirmation

As the README contains a full list of dependencies and the user of this
script is required to have administrator privileges, do not ask for any
further confirmation when installing system packages. That also allows
unattended runs of this script (called with privileges).

Change-Id: Icb7a0c30ac188e3701f7096e50ebb71b3c9d3dc6
Signed-off-by: Matthias Maennich <maennich@google.com>
diff --git a/abi/bootstrap b/abi/bootstrap
index e6cb841..bac3c73 100755
--- a/abi/bootstrap
+++ b/abi/bootstrap
@@ -32,7 +32,7 @@
 PACKAGES="autoconf elfutils libtool libxml2-dev libdw-dev pkg-config python3"
 # Install the dependencies.
 if ! dpkg -s ${PACKAGES} > /dev/null 2>&1 ; then
-    sudo apt-get install ${PACKAGES}
+    sudo apt-get install --yes ${PACKAGES}
 fi
 
 # Assert minimum package versions