various: fix make gh-action-test and update README

We have the new `./test/scripts/install-dependencies` helper
that centralizes the installation of the build dependencies.
So use it in the Containerfile and update the README to point
to it.

Author: mvo5

Containerfile

@@ -9,9 +9,7 @@ WORKDIR /setup
 COPY ./test/scripts ./test/scripts/
 COPY Schutzfile .
 RUN ./test/scripts/setup-osbuild-repo
-
-# NOTE: keep in sync with README.md#Contributing
-RUN dnf -y install krb5-devel go gpgme-devel osbuild-depsolve-dnf btrfs-progs-devel device-mapper-devel
+RUN ./test/scripts/install-dependencies
 
 COPY go.mod go.sum .
 RUN go mod download

README.md

@@ -48,13 +48,21 @@ required.
 
 #### Build requirements
 
-The build-requirements of the Go library for Fedora and rpm-based distributions are:
+The build-requirements of the Go library for Fedora and rpm-based
+distributions can be installed with:
 
-- `go`
-- `gpgme-devel`
+```console
+sudo ./test/scripts/install-dependencies
+```
 
 (see also [`Containerfile`](Containerfile) )
 
+The minimal dependencies are:
+
+- `go`
+- `gpgme-devel`
+- `libvirt-devel`
+
 Other dependencies only needed in some cases are:
 
 - `btrfs-progs-devel`, `device-mapper-devel`