zookeeper.service: option for package and add to environment

nixos/modules/services/misc/zookeeper.nix

@@ -106,10 +106,19 @@ in {
       '';
     };
 
+    package = mkOption {
+      description = "The zookeeper package to use";
+      default = pkgs.zookeeper;
+      defaultText = "pkgs.zookeeper";
+      type = types.package;
+    };
+
   };
 
 
   config = mkIf cfg.enable {
+    environment.systemPackages = [cfg.package];
+
     systemd.services.zookeeper = {
       description = "Zookeeper Daemon";
       wantedBy = [ "multi-user.target" ];
@@ -118,7 +127,7 @@ in {
       serviceConfig = {
         ExecStart = ''
           ${pkgs.jre}/bin/java \
-            -cp "${pkgs.zookeeper}/lib/*:${pkgs.zookeeper}/${pkgs.zookeeper.name}.jar:${configDir}" \
+            -cp "${cfg.package}/lib/*:${cfg.package}/${cfg.package.name}.jar:${configDir}" \
             ${escapeShellArgs cfg.extraCmdLineOptions} \
             -Dzookeeper.datadir.autocreate=false \
             ${optionalString cfg.preferIPv4 "-Djava.net.preferIPv4Stack=true"} \