[WIP] add checks for obsolete settings

[ghost]

This might fix #1698

When running make V=s GLUON_RELEASE="master" GLUON_TARGET="ar71xx-tiny" GLUON_DEVICES="tp-link-tl-wr840n-v2" (site conf of Freifunk Hamburg and Gluon master) the following output is printed eight times:

site.conf obsolete: opkg.lede is obsolete and could be removed, check the release notes and documentation please

I am not sure if print() is a good choice or if something like io.stderr:write() should be used
e.g. io.stderr:write(src .. ' obsolete: ' .. string.format(...) .. '\n') (but it is visible with V=s, only)

Also not sure if a generic text is fine or if it should be possible to describe what is wrong, add a link to the documentation/release notes, ... what do you think?

[mweinelt]

Being visible only when V=s is passed is probably not good enough.

[ghost]

@mweinelt where should it be visible? e.g. an error of the site config is visible via V=s only isn't it?

[neocturne]

One option would be to make obsolete settings a hard failure.

We currently don't have a good way to make warnings visible without V=s (or BUILD_LOG=1 for logging into files)... but I assume such a facility could be added to OpenWrt.

[rotanid]

hard failure should be OK as its easily fixable and clearly highlights something has to be done.

[ghost]

running

make -j 1 V=s GLUON_BRANCH=${GLUON_BRANCH} GLUON_TARGET=ar71xx-tiny GLUON_RELEASE=${GLUON_RELEASE}

with a probability setting will fail with

*** site.conf error: autoupdater.branches.stable.probability is obsolete Use GLUON_PRIORITY in site.mk instead.
postinst script ./usr/lib/opkg/info/gluon-autoupdater.postinst has failed with exit code 1

or with a opkg.lede setting will fail with

*** site.conf error: opkg.lede is obsolete Use opkg.openwrt instead.
postinst script ./usr/lib/opkg/info/gluon-core.postinst has failed with exit code 1

or a different obsolete setting '...' without a custom message will fail with

*** site.conf error: ... is obsolete and must be migrated or removed, check the release notes and documentation please

[neocturne]

Implementation looks ok. I think the following formatting/wording would look better:

*** site.conf error: ... is obsolete and must be migrated or removed. Please check the release notes and documentation for details.

*** site.conf error: autoupdater.branches.stable.probability is obsolete. Use GLUON_PRIORITY in site.mk instead.

[ghost]

@NeoRaider i reworded the message somehow. Not sure if it is okay like it is now: 38a10d5

Should that be documented somewhere? Are there docs for check_site available?