Don't install recommendeds with debootstrap

Change-Id: I0b48177acd0453be459755ced70c031ca3a29c6b
diff --git a/kokoro/rootfs.sh b/kokoro/rootfs.sh
index 1eec9ea..1a200b5 100644
--- a/kokoro/rootfs.sh
+++ b/kokoro/rootfs.sh
@@ -10,7 +10,7 @@
 # Debootstrap on 14.04 is very old and buggy. Update to the 16.04 version.
 echo "deb http://archive.ubuntu.com/ubuntu xenial main restricted universe multiverse" | sudo tee -a /etc/apt/sources.list
 sudo apt-get update
-sudo apt-get install -y debootstrap/xenial
+sudo apt-get install --no-install-recommends -y debootstrap/xenial
 
 export DEBOOTSTRAP_FETCH_TARBALL=false
 export ROOTFS_FETCH_TARBALL=false