btrfs-progs: Convert: Add support for rollback new convert behavior

btrfs-progs: Convert: Add support for rollback new convert behavior

Add support to rollback new btrfs-convert.

The support is quite easy unlike the new convert behavior, which in fact
makes the rollback less restricted.

The core is, rollback must support both old and new convert result.

For old convert, all fs image extents can be covered by any chunk type.
But any extents inside reserved range must be covered by chunk.
For new convert, all fs image extents are covered by data chunk.

Allowing any condition will just make another fail to pass.
So make the convert condition a little less restricted to allow both can
be converted.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>