Add the ZFS Test Suite

Add the ZFS Test Suite

Add the ZFS Test Suite and test-runner framework from illumos.
This is a continuation of the work done by Turbo Fredriksson to
port the ZFS Test Suite to Linux.  While this work was originally
conceived as a stand alone project integrating it directly with
the ZoL source tree has several advantages:

  * Allows the ZFS Test Suite to be packaged in zfs-test package.
    * Facilitates easy integration with the CI testing.
    * Users can locally run the ZFS Test Suite to validate ZFS.
      This testing should ONLY be done on a dedicated test system
      because the ZFS Test Suite in its current form is destructive.
  * Allows the ZFS Test Suite to be run directly in the ZoL source
    tree enabled developers to iterate quickly during development.
  * Developers can easily add/modify tests in the framework as
    features are added or functionality is changed.  The tests
    will then always be in sync with the implementation.

Full documentation for how to run the ZFS Test Suite is available
in the tests/README.md file.

Warning: This test suite is designed to be run on a dedicated test
system.  It will make modifications to the system including, but
not limited to, the following.

  * Adding new users
  * Adding new groups
  * Modifying the following /proc files:
    * /proc/sys/kernel/core_pattern
    * /proc/sys/kernel/core_uses_pid
  * Creating directories under /

Notes:
  * Not all of the test cases are expected to pass and by default
    these test cases are disabled.  The failures are primarily due
    to assumption made for illumos which are invalid under Linux.
  * When updating these test cases it should be done in as generic
    a way as possible so the patch can be submitted back upstream.
    Most existing library functions have been updated to be Linux
    aware, and the following functions and variables have been added.
    * Functions:
      * is_linux          - Used to wrap a Linux specific section.
      * block_device_wait - Waits for block devices to be added to /dev/.
    * Variables:            Linux          Illumos
      * ZVOL_DEVDIR         "/dev/zvol"    "/dev/zvol/dsk"
      * ZVOL_RDEVDIR        "/dev/zvol"    "/dev/zvol/rdsk"
      * DEV_DSKDIR          "/dev"         "/dev/dsk"
      * DEV_RDSKDIR         "/dev"         "/dev/rdsk"
      * NEWFS_DEFAULT_FS    "ext2"         "ufs"
  * Many of the disabled test cases fail because 'zfs/zpool destroy'
    returns EBUSY.  This is largely causes by the asynchronous nature
    of device handling on Linux and is expected, the impacted test
    cases will need to be updated to handle this.
  * There are several test cases which have been disabled because
    they can trigger a deadlock.  A primary example of this is to
    recursively create zpools within zpools.  These tests have been
    disabled until the root issue can be addressed.
  * Illumos specific utilities such as (mkfile) should be added to
    the tests/zfs-tests/cmd/ directory.  Custom programs required by
    the test scripts can also be added here.
  * SELinux should be either is permissive mode or disabled when
    running the tests.  The test cases should be updated to conform
    to a standard policy.
  * Redundant test functionality has been removed (zfault.sh).
  * Existing test scripts (zconfig.sh) should be migrated to use
    the framework for consistency and ease of testing.
  * The DISKS environment variable currently only supports loopback
    devices because of how the ZFS Test Suite expects partitions to
    be named (p1, p2, etc).  Support must be added to generate the
    correct partition name based on the device location and name.
  * The ZFS Test Suite is part of the illumos code base at:
    https://github.com/illumos/illumos-gate/tree/master/usr/src/test

Original-patch-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #6
Closes #1534