ZTS: Fix in-tree dbufstats test case

[behlendorf]

Motivation and Context

Issue #9118

Description

Commit a887d65 updated the dbufstats such that escalated privileges
are required. Since all tests under cli_user are run with normal
privileges move this test case to a location where it will be run
required privileges.

How Has This Been Tested?

$ ./scripts/zfs-tests.sh -T arc
Test: /home/behlendo/src/git/zfs/tests/zfs-tests/tests/functional/arc/setup (run as root) [00:01] [PASS]
Test: /home/behlendo/src/git/zfs/tests/zfs-tests/tests/functional/arc/dbufstats_001_pos (run as root) [00:01] [PASS]
Test: /home/behlendo/src/git/zfs/tests/zfs-tests/tests/functional/arc/dbufstats_002_pos (run as root) [00:00] [PASS]
Test: /home/behlendo/src/git/zfs/tests/zfs-tests/tests/functional/arc/dbufstats_003_pos (run as root) [00:01] [PASS]
Test: /home/behlendo/src/git/zfs/tests/zfs-tests/tests/functional/arc/cleanup (run as root) [00:00] [PASS]

Results Summary
PASS	   5

Running Time:	00:00:06
Percent passed:	100.0%
Log directory:	/var/tmp/test_results/20190821T130645

Tests with results other than PASS that are expected:

Tests with result of PASS that are unexpected:

Tests with results other than PASS that are unexpected:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.

[c0d3z3r0]

lgtm

[codecov]

Codecov Report

Merging #9196 into master will decrease coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #9196      +/-   ##
==========================================
- Coverage   79.22%   79.14%   -0.09%     
==========================================
  Files         400      400              
  Lines      122001   122001              
==========================================
- Hits        96656    96553     -103     
- Misses      25345    25448     +103

Flag	Coverage Δ
#kernel	79.72% <ø> (-0.02%)	⬇️
#user	66.94% <ø> (-0.1%)	⬇️

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