Remove old Lua code

[cmouse]

Short description

Removes all old lua code from PowerDNS auth server, and provides codesharing between auth and recursor.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled and tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[cmouse]

Currently stuck at __tostring

The LuaContext used keeps the functions available stored in global table. I have not yet been able to decipher how the mapping between object<=>function name<=>function is done, but it seems to rely on pointer to the proper member function. This makes things difficult. I am assuming that there is, somewhere, some way to find out what object:function is, and that you can actually figure out this on run-time.

It is possible to get a live pointer to the C++ object in question, but I have not yet found a way to execute ::toString only if there is such member function, or figure out how to see if there is a _tostring function mapped for the object or not.

It is probably easier to find out the latter than the first, since this information is kept at global function table stored somewhere.

[cmouse]

Please merge #5468 first

[cmouse]

Also pending on ahupowerdns/luawrapper#35

[cmouse]

Not sure why the test fails, I cannot make it fail locally.

[cmouse]

The reason the tests fail is that recursor test uses pdns auth server 4.0.4, which is obviously not going to include the lua changes done here. I am not sure how to resolve this problem, please advise.

[Habbie]

Approved with one question. This looks good, nice chunk of work. I'd like either a second reviewer, or to merge this after both 4.1.0 releases.

[Habbie]

Does this need a documentation update?

[cmouse]

no, it's just explicitly documented here.

[Habbie]

In the "ext/luawrapper: Synchronize with upstream" commit message, can you clarify synchronize? If it is a full sync, please mention the commit you synced with. If it's an import of one patch, please mention that.