test: New test: test_start_stop_service

Add a new test that verifies that Finit will:
- Start a service that's been added to the config
- Stop the service once it's removed from the config

The second step is currently failing.

Signed-off-by: Jacques de Laval <jacques@de-laval.se>

test/testenv_exec.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+
+set -eu
+
+if [ "$#" -lt 2 ]; then
+    echo "Usage:"
+    echo "  $0 [target-pid] [command [arguments]]"
+    exit 1
+fi
+target="$1"
+shift
+
+TEST_DIR=$(dirname "$0")
+TESTS_ROOT="$(pwd)/${TEST_DIR}/test_root"
+
+export PATH=/sbin:/bin
+nsenter \
+    --preserve-credentials \
+    --user \
+    --mount \
+    --uts \
+    --ipc \
+    --net \
+    --pid \
+    -w -t "$target" \
+    chroot "$TESTS_ROOT" "$@"