timeout: handle arguments for the command to run

To prevent clap from parsing flags for the command to run as flags for
timeout, remove the "args" positional argument, but allow to pass flags
via the "command" positional arg.

tests/by-util/test_timeout.rs

@@ -9,3 +9,11 @@ fn test_subcommand_return_code() {
 
     new_ucmd!().arg("1").arg("false").run().status_code(1);
 }
+
+#[test]
+fn test_command_with_args() {
+    new_ucmd!()
+        .args(&["1700", "echo", "-n", "abcd"])
+        .succeeds()
+        .stdout_only("abcd");
+}