[pkg] do not include all files in spec

our spec files conflict with filesystem package in centos7: we set permission
755 for /usr/bin and /usr/lib whereas filesystem set it to 555.

So to be compatible with both centos7 and others we simply ignore theses
directories

cubicweb-link.spec

@@ -43,4 +43,4 @@
 
 %files
 %defattr(-, root, root)
-/*
+%{_prefix}/share/cubicweb*