zfs_receive_010_pos: change dd arguments

The dd command as written will not create a hole in the file.
Additionally, the stride argument isn't understood by dd so
it's replaced with seek which isn't equivilant but will result in
a single whole which is sufficient for the test case. Finally,
conv=notrunc is added to avoid truncating the file.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: George Melikov <mail@gmelikov.ru>
Closes #6023