OpenZFS 7290 - ZFS test suite needs to control what utilities it can run

OpenZFS 7290 - ZFS test suite needs to control what utilities it can run

Authored by: John Wren Kennedy <john.kennedy@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Approved by: Gordon Ross <gordon.w.ross@gmail.com>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>
Porting Notes:
- Utilities which aren't available under Linux have been removed.
- Because of sudo's default secure path behavior PATH must be
  explicitly reset at the top of libtest.shlib.  This avoids the
  need for all users to customize secure path on their system.
- Updated ZoL infrastructure to manage constrained path
- Updated all test cases
- Check permissions for usergroup tests
- When testing in-tree create links under bin/
- Update fault cleanup such that missing files during
  cleanup aren't fatal.
- Configure su environment with constrained path

OpenZFS-issue: https://www.illumos.org/issues/7290
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/1d32ba6
Closes #5903