docker/debian: Add sudo to ci image (envoyproxy#451)

Signed-off-by: Ryan Northey <ryan@synca.io>

Author: phlax

docker/linux/debian/fun.sh

@@ -15,7 +15,7 @@ COMMON_PACKAGES=(
     libtinfo5
     patch)
 DEV_PACKAGES=()
-CI_PACKAGES=(git gosu)
+CI_PACKAGES=(git gosu sudo)
 DEBIAN_PACKAGES=(
     aspell
     aspell-en