nixos: remove rsync from base install and add explicit path in nixos-install

As per 60b3f95ad8 (commitcomment-18507812)

nixos/modules/config/system-path.nix

@@ -34,7 +34,6 @@ let
       config.programs.ssh.package
       pkgs.perl
       pkgs.procps
-      pkgs.rsync
       pkgs.strace
       pkgs.su
       pkgs.time

nixos/modules/installer/tools/nixos-install.sh

@@ -175,7 +175,7 @@ if ! NIX_DB_DIR=$mountPoint/nix/var/nix/db nix-store --check-validity @nix@ 2> /
     for i in $(@perl@/bin/perl @pathsFromGraph@ @nixClosure@); do
         echo "  $i"
         chattr -R -i $mountPoint/$i 2> /dev/null || true # clear immutable bit
-        rsync -a $i $mountPoint/nix/store/
+        @rsync@/bin/rsync -a $i $mountPoint/nix/store/
     done
 
     # Register the paths in the Nix closure as valid.  This is necessary

nixos/modules/installer/tools/tools.nix

@@ -21,7 +21,7 @@ let
     name = "nixos-install";
     src = ./nixos-install.sh;
 
-    inherit (pkgs) perl pathsFromGraph;
+    inherit (pkgs) perl pathsFromGraph rsync;
     nix = config.nix.package.out;
     cacert = "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt";