odhcp-script: delete stale dirs from previous runs

This requires adding LFS as a dependency because native Lua has
no way to iterate a directory, but it seems to be Not Huge and
hopefully we'll have other uses for it

pkgs/odhcp-script/test.sh

@@ -9,6 +9,11 @@ cleanup(){
 trap 'exit 1' INT HUP QUIT TERM ALRM USR1
 trap 'cleanup' EXIT
 
+# call the script twice with different state, to test that it cleans
+# out old values when it runs again
+
+(set -a; .  ./test.env ; ADDRESSES=2001:80:111:111:0:fff:123:567/128,3600,7200 SERVICE_STATE=$statedir fennelrepl odhcp6-script.fnl ppp0 bound)  10>&1
+
 (set -a; . ./test.env ; SERVICE_STATE=$statedir fennelrepl odhcp6-script.fnl ppp0 bound)  10>&1
 
 (cd $statedir && find . -type f | xargs grep '' | sort) > actual