Disable vdev_zaps_004_pos

[behlendorf]

Description

Occasionally observed failure of vdev_zaps_004_pos due to the test
case not being 100% reliable. In order to prevent false positives
disable this test case until it can be made reliable.

Motivation and Context

Issue #6935

How Has This Been Tested?

Buildbot

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.
• Change has been approved by a ZFS on Linux member.

[codecov]

Codecov Report

Merging #6936 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #6936      +/-   ##
=========================================
- Coverage   75.11%   75.1%   -0.02%     
=========================================
  Files         296     296              
  Lines       95457   95457              
=========================================
- Hits        71704   71691      -13     
- Misses      23753   23766      +13

Flag	Coverage Δ
#kernel	74.6% <ø> (-0.15%)	⬇️
#user	67.28% <ø> (+0.29%)	⬆️

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