uucore: process: fix exit status processing (#1743)

* uucore: process: fix exit status processing

* tests: timeout: check whether subcommand exit codes are returned

tests/by-util/test_timeout.rs

@@ -1 +1,18 @@
-// ToDO: add tests
+use crate::common::util::*;
+
+// FIXME: this depends on the system having true and false in PATH
+//        the best solution is probably to generate some test binaries that we can call for any
+//        utility that requires executing another program (kill, for instance)
+#[test]
+fn test_subcommand_retcode() {
+    new_ucmd!()
+        .arg("1")
+        .arg("true")
+        .succeeds();
+
+    new_ucmd!()
+        .arg("1")
+        .arg("false")
+        .run()
+        .status_code(1);
+}