Add packages on Linux requested by Envoy.

https://github.com/bazelbuild/continuous-integration/issues/218
diff --git a/buildkite/setup-ubuntu.sh b/buildkite/setup-ubuntu.sh
index 8ba7d3c..3c7afd8 100755
--- a/buildkite/setup-ubuntu.sh
+++ b/buildkite/setup-ubuntu.sh
@@ -61,7 +61,14 @@
   libcurl3-dev
   swig
 
-  # Infra stuff.
+  # Required by Envoy: https://github.com/bazelbuild/continuous-integration/issues/218
+  automake
+  autotools-dev
+  cmake
+  libtool
+  m4
+
+  # Required by our infrastructure.
   lvm2
 )
 apt-get -qqy install "${packages[@]}" > /dev/null