Add mock 2.6 to workarounds, drop kernel for F31 and F32
Kernel updates for F31 and F32 went stable so they can come out.
mock 2.6 fixes the bug that occurs when /etc/resolv.conf is a
dangling symlink - this breaks the live_build test.
Signed-off-by: Adam Williamson <awilliam@redhat.com>