Use a timeout of 1s when testing the sandbox on Linux.

This is to avoid hanging there forever in case the system is set up
incorrectly.
1s should be plenty to run `/bin/true`.

Fixes bazelbuild#15373.

src/main/java/com/google/devtools/build/lib/sandbox/LinuxSandboxedSpawnRunner.java

@@ -88,7 +88,7 @@ public static boolean isSupported(final CommandEnvironment cmdEnv) throws Interr
   private static boolean computeIsSupported(CommandEnvironment cmdEnv, Path linuxSandbox)
       throws InterruptedException {
     ImmutableList<String> linuxSandboxArgv =
-        LinuxSandboxUtil.commandLineBuilder(linuxSandbox, ImmutableList.of("/bin/true")).build();
+        LinuxSandboxUtil.commandLineBuilder(linuxSandbox, ImmutableList.of("-T", "1", "--", "/bin/true")).build();
     ImmutableMap<String, String> env = ImmutableMap.of();
     Path execRoot = cmdEnv.getExecRoot();
     File cwd = execRoot.getPathFile();