[dist] change homedir of user 'obsservicerun'

With this commit we change $HOME of the user 'obsservicerun' from
/usr/lib/obs to /srv/obs/service. /srv/obs/service is owned by 'obsservicerun'
by default. It should avoid problems for services using git via ssh.

dist/obs-server.spec

@@ -521,7 +521,7 @@ make -C dist test
 
 %pre
 getent passwd obsservicerun >/dev/null || \
-    /usr/sbin/useradd -r -g obsrun -d /usr/lib/obs -s %{sbin}/nologin \
+    /usr/sbin/useradd -r -g obsrun -d %{obs_backend_data_dir}/service -s %{sbin}/nologin \
     -c "User for the build service source service" obsservicerun
 
 %service_add_pre obsscheduler.service