[libvirt] Remove bashisms from libvirt-guests

Hi, The attached patch removes bashisms from libvirt-guests. TEXTDOMAINDIR is not specified, so system default will be used ("/usr/share/locale" on Debian, I don't know if it's the same on Fedora). "xgettext -L Shell" output is the same with gettext shell functions as with $"..." deprecated Bash-specific syntax. Please generate po files somewhere in the source tree. Thank you, -- Laurent Léonard