gtk interface building resulted in no gtk interface being built for some
reason, and reference working set ups all used qt, so this commit
switches interface to qt and fights with bugs that come from this
change.

QGtkStyle (needed for Proview-R) support in qt4 needs glib.
However, config script for qt4 is written in such a way that if glib is not
requested but QGtkStyle is requested, it just silently turns QGtkStyle off.

On the other hand, if glib is requested explicitly, then if script fails to
enable QGtkStyle it reports an error properly.
I think it was a bug in qt4 error reporting mechanism that made compilation go
smoothly even though requested QGtkStyle was never provided.
Nobody will fix it now though.

Anyway, this commit properly enables glib and fights with everything that rises
up as a result of this, leading to successfull QGtkStyle support.

https:// link just works more reliably as I found after several timeouts.

But I still have no idea why the second db folder spawns right inside
the frst one.

straighetend the configs:
no more custom source packages
using xvfb for proview compilation (easier)
fix bug with pwr pre-build process killing itself

Future Cython+ work will use it.

Fix for #20200514-218C705 - \[testnode\] frontend for log access

Depends on nexedi/erp5!1304

See merge request nexedi/slapos!848

This fixes the nextcloud SR, which was broken by
commit 92779bf4
(mariadb is not a part anymore).

This fixes commit a62e5e7b.
See also commit 491e6e28.

And set it as log_frontend_url in testnode config

Just add the following 2 lines in a SR:

[mariadb]
location = ${mariadb-10.4:location}

It does not build with GCC 8.2

Going Go1.14.9 -> Go1.14.10 brings in compiler and runtime fixes
including fix for crash in garbage-collector due to race condition:

https://github.com/golang/go/issues/40642
https://github.com/golang/go/issues/40641

Tested on helloworld SR.

See merge request nexedi/slapos!844

validators.url is enough, even for Caddy, to check that URL is correct, and
caddy_backend_url_validator was introduced before validators.

Also calling an external command for each slave takes a lot of time.