Previously with squash module, some binaries will be reinstalled, but
stripping happens before that so new installed binaries is not stripped.
So adjust the squash and strip order, ensure new installed binaries are
stripped just the same way with the old binaries.
Also split squash into two stage to make the split easier, move the
squash temp dir into initdir so stripping will cover that too,
and print more usefule message.
Signed-off-by: Kairui Song <kasong@redhat.com>