MFV r316934: 7340 receive manual origin should override automatic origin

MFV r316934: 7340 receive manual origin should override automatic origin

illumos/illumos-gate@ed4e7a6a5cbc5e8986dc649ad54435210487b102
https://github.com/illumos/illumos-gate/commit/ed4e7a6a5cbc5e8986dc649ad54435210487b102

https://www.illumos.org/issues/7340
  When -o origin=<snapshot> is specified as part of a ZFS receive, that origin
  should override the automatic detection in libzfs.

Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Paul Dagnelie <pcd@delphix.com>

MFC after:	3 weeks