pipeline: detect host instead of using org.osbuild.host

Detect the host dynamically from os-release(5) instead of relying on the
`org.osbuild.host` symlink.

It is awkward to install a symlink that tells osbuild which distro is is
running on, when there is a standard way to detect this.

This makes it easier to run osbuild from sources and removes the need to
include every host in the spec file. The latter became hard to do,
because there's no obvious way to distinguish RHEL minor releases.

.gitignore

@@ -10,8 +10,6 @@ __pycache__
 
 /test/.vagrant
 
-/runners/org.osbuild.host
-
 /.vscode
 /.idea
 /.gdb_history