nixos/tests/installer: fix

Since #528209 split procps into outputs, the nix-env invocation
started trying to install said outputs, which are not available
in the closure by accident like procps itself was.

Switch to using hello as the "example package", as it is very
unlikely to randomly grow more outputs and break things,
and also add it to extraDependencies to ensure it's available
to be installed.

nixos/tests/installer.nix

@@ -41,7 +41,7 @@ let
         documentation.enable = false;
 
         # To ensure that we can rebuild the grub configuration on the nixos-rebuild
-        system.extraDependencies = with pkgs; [ stdenvNoCC ];
+        system.extraDependencies = with pkgs; [ stdenvNoCC hello ];
 
         boot.initrd.systemd.enable = ${boolToString systemdStage1};
 
@@ -278,14 +278,14 @@ let
           target.succeed("nix-store --verify --check-contents >&2")
 
       with subtest("Check whether the channel works"):
-          target.succeed("nix-env -iA nixos.procps >&2")
-          assert ".nix-profile" in target.succeed("type -tP ps | tee /dev/stderr")
+          target.succeed("nix-env -iA nixos.hello >&2")
+          assert ".nix-profile" in target.succeed("type -tP hello | tee /dev/stderr")
 
       with subtest(
           "Check that the daemon works, and that non-root users can run builds "
           "(this will build a new profile generation through the daemon)"
       ):
-          target.succeed("su alice -l -c 'nix-env -iA nixos.procps' >&2")
+          target.succeed("su alice -l -c 'nix-env -iA nixos.hello' >&2")
 
       with subtest("Configure system with writable Nix store on next boot"):
           # we're not using copy_from_host here because the installer image
@@ -744,6 +744,7 @@ let
                   desktop-file-utils
                   docbook5
                   docbook_xsl_ns
+                  hello
                   kbd.dev
                   kmod.dev
                   libarchive.dev