Fix filesystem destroy with receive_resume_token

It is possible that the given DS may have hidden child (%recv)
datasets - "leftovers" resulting from the previously interrupted
'zfs receieve'. Try to remove the hidden child (%recv) and after
that try to remove the target dataset. If the hidden child
(%recv) does not exist the original error (EEXIST) will be returned.

Signed-off-by: Roman Strashkin <roman.strashkin@nexenta.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4818