[packman] Unify vendors for libzypp

[Christian Morales Vega]

Not sure about the best way to archieve this. But at least one time a
package from Packman changed the vendor string in a 11.0 update.
The thing is, for libzypp to inform about updates there can't be a vendor
change. So I needed to create a /etc/zypp/vendors.d/packman file with:
"[main]

vendors=http://packman.links2linux.de,packman.links2linux.de,Packman"
(I did a quick look at libzypp source code for this, don't ask me where the
file format is explained).

Should a package be created with this file? There exists some way to make
users install it?