Fix the way openSUSE finds the tree

It has no kickstart so use the same logic as debian/ubuntu. Extract the
tree location from ks_meta[tree].

(REVIEW with diff -b (ignore space changes))
Two more places to put "opensuse" beside "suse".

Found with grep. I think they belong here.
Merge pull request #771 from jansenm/opensuse-fixes

Opensuse fixes