OpenZFS 8972 - zfs holds: In scripted mode, do not pad columns with spaces

Authored by: Allan Jude <allanjude@freebsd.org>
Approved by: Dan McDonald <danmcd@joyent.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Melikov <mail@gmelikov.ru>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

OpenZFS-issue: https://www.illumos.org/issues/8972
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/3aace5c077
Closes #7063