nixosTests.docker-tools: Use unique binary in test case

nixos/tests/docker-tools.nix

@@ -388,7 +388,7 @@ import ./make-test-python.nix ({ pkgs, ... }: {
 
     with subtest("The image contains store paths referenced by the fakeRootCommands output"):
         docker.succeed(
-            "docker run --rm ${examples.layeredImageWithFakeRootCommands.imageName} /hello/bin/hello"
+            "docker run --rm ${examples.layeredImageWithFakeRootCommands.imageName} /hello/bin/layeredImageWithFakeRootCommands-hello"
         )
 
     with subtest("exportImage produces a valid tarball"):

pkgs/build-support/docker/examples.nix

@@ -507,7 +507,11 @@ rec {
     fakeRootCommands = ''
       mkdir -p ./home/jane
       chown 1000 ./home/jane
-      ln -s ${pkgs.pkgsStatic.hello} ./hello
+      ln -s ${pkgs.hello.overrideAttrs (o: {
+        # A unique `hello` to make sure that it isn't included via another mechanism by accident.
+        configureFlags = o.configureFlags or "" + " --program-prefix=layeredImageWithFakeRootCommands-";
+        doCheck = false;
+      })} ./hello
     '';
   };