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

Nextcloud's redis is causing `AF_UNIX path too long` on test nodes.

The first commit to adapt this test to slapos.testing was incomplete.
Now that nextcloud is fixed, we saw a few mistakes and python3
incompatibilities that are fixed in this commit.

This reverts commit 4636f49f.

This reverts commit 97884c30.

Package like lm-sensors, which depends on the kernel, shall be provided
by the OS.

/reviewed-on nexedi/slapos!642

It is proven to work on Debian 10.

/reviewed-on nexedi/slapos!640

slapos node collect require lmsensors, so use those ones provied with slapos
component.

/reviewed-on nexedi/slapos!641

Otherwise it will be installed without our special part, using system
curl.

/reviewed-on nexedi/slapos!639

/reviewed-on !635

also drop test_nextcloud_promises as promises are now checked by
framework.

/reviewed-on nexedi/slapos!636