generate-svn-snapshot: run svn-buildpackage in subshell and move files to orig dir
generate-svn-snapshot: run svn-buildpackage in subshell and move files to orig dir

If we switch the directory we might end up in the wrong directory
for further actions, so run all the commands around svn-buildpackage
in a subshell.

Also replace the --svn-move command with --svn-move-to to place
the artifact files in the original directory, otherwise the files
might be placed in the wrong directory if $branch is set and used.

tanglu-org/jenkins-tanglu-buildkit,jbfavre/jenkins-debian-glue,kartikm/jenkins-debian-glue,jbfavre/jenkins-debian-glue,tonin/jenkins-debian-glue,bmiklautz/jenkins-debian-glue,hetznerZA/jenkins-debian-glue,wikimedia/operations-debs-jenkins-debian-glue,vorlock/jenkins-debian-glue,mika/jenkins-debian-glue,linuxmaniac/jenkins-debian-glue,bmiklautz/jenkins-debian-glue,hashar/jenkins-debian-glue,tanglu-org/jenkins-tanglu-buildkit,hetznerZA/jenkins-debian-glue,cclausen/jenkins-debian-glue,n054/jenkins-debian-glue,mika/jenkins-debian-glue,tonin/jenkins-debian-glue,vorlock/jenkins-debian-glue,zeha/jenkins-debian-glue,hashar/jenkins-debian-glue,webtrekk-kane/jenkins-debian-glue,webtrekk-kane/jenkins-debian-glue,linuxmaniac/jenkins-debian-glue,n054/jenkins-debian-glue,zeha/jenkins-debian-glue,wikimedia/operations-debs-jenkins-debian-glue,cclausen/jenkins-debian-glue,kartikm/jenkins-debian-glue,tanglu-org/jenkins-tanglu-buildkit