btrfs: sparse copy between different filesystems/mountpoints

btrfs: sparse copy between different filesystems/mountpoints

Check if creating a sparse copy ("reflink") of a file on btrfs
expectedly fails when it's done between different filesystems or
different mount points of the same filesystem.

For both situations, these actions are executed:
   - Copy a file with the reflink=auto option.
     A normal copy should be created.
   - Copy a file with the reflink=always option. Should result in
     error.

[sandeen: mostly cosmetic changes]

Signed-off-by: Koen De Wit <koen.de.wit@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>