Make lintian-junit-report ruby 1.8 safe

The changes from commits 7a974f4f and 21b8527d don't work when
running on Ruby 1.8:

| /usr/bin/lintian-junit-report:85:in `popen': can't convert Array into String (TypeError)
| 	from /usr/bin/lintian-junit-report:85
lintian-junit-report: quote XML strings