Motivation for this change

In elasticsearch5, elasticsearch-plugin fails with the error message:

Error: Could not find or load main class org.elasticsearch.plugins.PluginCli

Since it forces the class path to ES_HOME/lib/*, and makes it difficult to override. This change makes the class path be specified by ES_CLASSPATH, like the main elasticsearch script, so the wrapper can set it to the correct path.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.