OpenZFS 7404 - rootpool_007_neg, bootfs_006_pos and bootfs_008_neg tests fail with...

OpenZFS 7404 - rootpool_007_neg, bootfs_006_pos and bootfs_008_neg tests fail with the loader project bits

Authored by: Toomas Soome <tsoome@me.com>
Reviewed by: Igor Kozhukhov <igor@dilos.org>
Reviewed by: Marcel Telka <marcel@telka.sk>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>
Porting Notes:
- Removed gzip and zle compression restriction on bootfs
  datasets.  Grub added support for these long ago.  Ay
  version of grub which understands lz4 also supports this.
- Enabled rootpool tests in runfile but skipped by default
  in setup on Linux since they modify the rootpool.
- bootfs_006_pos.ksh, striped pools are allowed as bootfs.

OpenZFS-issue: https://www.illumos.org/issues/7404
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/55a424c
Closes #5982