fix(*) improve Lua paths for dev environments (Kong#2845)

Historically, and so far, with success, the Lua path was always setup so
that when in the `kong/` repository, the local files take precedence over
any system-wide installation of code. This includes all Lua files in
this repository, in the following environments:

- The Kong CLI
- Running Kong instances
- Running tests suites

Prior to this, we were having several issues with some disparities in
the Lua path setups. Disparities that became more apparent after some
recent changes, possibly related to the Homebrew Formula updates made
with the prefix and the LuaRocks system tree.

We here attempt to unify the various places in which we specify the Lua
path values for each of the aforementioned environments.

Following this change, our Lua path should look like so in all
environments:

    # inserted by bin/kong in CLI and lua_package_path in configuration
    # used for development
    ./?.lua;
    ./?/init.lua;
    # inserted by OpenResty (lua-resty-core in lualib + unused site)
    /usr/local/Cellar/openresty/1.11.2.4/site/lualib/?.lua;
    /usr/local/Cellar/openresty/1.11.2.4/site/lualib/?/init.lua;
    /usr/local/Cellar/openresty/1.11.2.4/lualib/?.lua;
    /usr/local/Cellar/openresty/1.11.2.4/lualib/?/init.lua;
    # inserted by LuaRocks (user tree)
    /Users/chasum/.luarocks/share/lua/5.1/?.lua;
    /Users/chasum/.luarocks/share/lua/5.1/?/init.lua;
    # inserted by LuaRocks (system tree used by Homebrew)
    /usr/local/opt/kong/share/lua/5.1/?.lua;
    /usr/local/opt/kong/share/lua/5.1/?/init.lua;
    # Inserted by LuaRocks (luarocks rocks is installed there)
    /usr/local/Cellar/luarocks/2.4.2/share/lua/5.1/?.lua;
    # A default path from the VM
    ./?.lua;
    # LuaJIT introspection lib
    /usr/local/Cellar/openresty/1.11.2.4/luajit/share/luajit-2.1.0-beta2/?.lua;
    # Another default path from the VM I think
    /usr/local/share/lua/5.1/?.lua;
    /usr/local/share/lua/5.1/?/init.lua;
    # Yet another default path from the VM (I think)
    # <INSTALL_PREFIX>/share/lua/<VERSION>
    /usr/local/Cellar/openresty/1.11.2.4/luajit/share/lua/5.1/?.lua;
    /usr/local/Cellar/openresty/1.11.2.4/luajit/share/lua/5.1/?/init.lua;

Note: to avoid having to keep using the `kong/?.lua` value which was
only being used to load the main `kong.lua` module, we had two possible
approaches: either change all of the `require "kong"` statements, which
would be breaking because have to update the Nginx template, either
finally make the main module adhere to our `init.lua` convention,
already followed across the codebase.

.busted

@@ -1,5 +1,5 @@
 return {
   default = {
-    lpath = "./?.lua;"
+    lpath = "./?.lua;./?/init.lua;"
   }
 }

bin/busted

@@ -7,7 +7,5 @@ require("kong.core.globalpatches")({
   rbusted = true
 })
 
-package.path = "?/init.lua;"..package.path
-
 -- Busted command-line runner
 require 'busted.runner'({ standalone = false })

bin/kong

@@ -2,6 +2,6 @@
 
 require "luarocks.loader"
 
-package.path = "?/init.lua;"..package.path
+package.path = "./?.lua;./?/init.lua;" .. package.path
 
 require("kong.cmd.init")(arg)

kong-0.11.0-0.rockspec

@@ -34,7 +34,7 @@ dependencies = {
 build = {
   type = "builtin",
   modules = {
-    ["kong"] = "kong/kong.lua",
+    ["kong"] = "kong/init.lua",
     ["kong.meta"] = "kong/meta.lua",
     ["kong.constants"] = "kong/constants.lua",
     ["kong.singletons"] = "kong/singletons.lua",

kong/templates/kong_defaults.lua

@@ -80,6 +80,6 @@ lua_code_cache = on
 lua_socket_pool_size = 30
 lua_ssl_trusted_certificate = NONE
 lua_ssl_verify_depth = 1
-lua_package_path = ?/init.lua;./kong/?.lua
+lua_package_path = ./?.lua;./?/init.lua;
 lua_package_cpath = NONE
 ]]

spec/01-unit/003-prefix_handler_spec.lua

@@ -57,7 +57,7 @@ describe("NGINX conf compiler", function()
   describe("compile_kong_conf()", function()
     it("compiles the Kong NGINX conf chunk", function()
       local kong_nginx_conf = prefix_handler.compile_kong_conf(helpers.test_conf)
-      assert.matches("lua_package_path '?/init.lua;./kong/?.lua;;';", kong_nginx_conf, nil, true)
+      assert.matches("lua_package_path './?.lua;./?/init.lua;;;'", kong_nginx_conf, nil, true)
       assert.matches("lua_code_cache on;", kong_nginx_conf, nil, true)
       assert.matches("listen 0.0.0.0:9000;", kong_nginx_conf, nil, true)
       assert.matches("listen 0.0.0.0:9001;", kong_nginx_conf, nil, true)

spec/kong_tests.conf

@@ -21,8 +21,6 @@ anonymous_reports = off
 
 dns_hostsfile = spec/fixtures/hosts
 
-lua_package_path = ?/init.lua;./kong/?.lua
-
 nginx_worker_processes = 1
 nginx_optimizations = off