Only run system tests as root in developer mode

Running system tests with root privileges is potentially dangerous.
Only allow it when explicitly requested (by building with
--enable-developer).

(cherry picked from commit 3ef106f6)

bin/tests/system/run.sh

@@ -16,6 +16,11 @@
 SYSTEMTESTTOP="$(cd -P -- "$(dirname -- "$0")" && pwd -P)"
 . $SYSTEMTESTTOP/conf.sh
 
+if [ "`id -u`" -eq "0" ] && ! ${NAMED} -V | grep -q -F -- "enable-developer"; then
+	echofail "Refusing to run test as root. Build with --enable-developer to override." >&2
+	exit 1
+fi
+
 export SYSTEMTESTTOP
 
 stopservers=true