[pkg] do not include toplevel directories in rpm (closes #10362119)
Our spec file conflicts with the filesystem package in centos7: we set
permissions to 0755 for /usr/bin and /usr/lib whereas filesystem sets
them to 0555.
So to be compatible with both centos7 and others we simply ignore these
directories.
"""cubicweb-%(cubename)s application package
%(longdesc)s
"""