build: Fix default network generation on FreeBSD
build: Fix default network generation on FreeBSD

FreeBSD's sed(1) doesn't support using "\n" to insert a newline,
so the installed default.xml file ends up containing a literal
"n" between tags; to work around this problem, add a tr(1)
invocation as suggested by the sed FAQ[1].

[1] http://sed.sourceforge.net/sedfaq4.html (4.1 c)

jardasgit/libvirt,jfehlig/libvirt,datto/libvirt,crobinso/libvirt,andreabolognani/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,crobinso/libvirt,datto/libvirt,eskultety/libvirt,taget/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,eskultety/libvirt,olafhering/libvirt,olafhering/libvirt,zippy2/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,jardasgit/libvirt,jfehlig/libvirt,nertpinx/libvirt,libvirt/libvirt,jardasgit/libvirt,andreabolognani/libvirt,olafhering/libvirt,datto/libvirt,libvirt/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,olafhering/libvirt,datto/libvirt,crobinso/libvirt,jardasgit/libvirt,crobinso/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,andreabolognani/libvirt,eskultety/libvirt,libvirt/libvirt,eskultety/libvirt,jardasgit/libvirt,taget/libvirt,fabianfreyer/libvirt,zippy2/libvirt,libvirt/libvirt,taget/libvirt,fabianfreyer/libvirt,taget/libvirt,nertpinx/libvirt,andreabolognani/libvirt,zippy2/libvirt,nertpinx/libvirt,zippy2/libvirt,VenkatDatta/libvirt,eskultety/libvirt,datto/libvirt,taget/libvirt