Add more sanity testing for zdb input args

[shartse]

Motivation and Context

There's a lot going on in ZDB, in the past as I've expanded it's features I've accidentally introduced regressions. I decided to take a stab at extending some of our testing.

Description

Add positive argument testing to confirm that flags that we expect to be available don't result in failures or crashes.

Modify the existing negative arg test to have a more explicit name and correct the test by adding a pool argument to the zdb invocation (some tests with valid flags were erroneously passing because they were missing the pool arg).

How Has This Been Tested?

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.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[codecov-io]

Codecov Report

Merging #10243 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10243      +/-   ##
==========================================
- Coverage   79.28%   79.27%   -0.01%     
==========================================
  Files         389      389              
  Lines      123402   123402              
==========================================
- Hits        97834    97823      -11     
- Misses      25568    25579      +11     

Flag	Coverage Δ
#kernel	79.86% <ø> (-0.04%)	⬇️
#user	65.62% <ø> (+1.20%)	⬆️

Impacted Files	Coverage Δ
module/os/linux/spl/spl-zlib.c	55.35% <0.00%> (-28.58%)	⬇️
cmd/zdb/zdb_il.c	30.86% <0.00%> (-24.08%)	⬇️
cmd/ztest/ztest.c	76.84% <0.00%> (-3.94%)	⬇️
module/zcommon/zfs_fletcher.c	75.65% <0.00%> (-2.64%)	⬇️
module/zfs/zio_compress.c	89.74% <0.00%> (-2.57%)	⬇️
module/zfs/dsl_synctask.c	92.40% <0.00%> (-2.54%)	⬇️
module/os/linux/zfs/vdev_file.c	80.37% <0.00%> (-1.87%)	⬇️
module/icp/api/kcf_mac.c	37.14% <0.00%> (-1.72%)	⬇️
lib/libzfs/libzfs_changelist.c	85.15% <0.00%> (-1.18%)	⬇️
module/zcommon/zfs_uio.c	87.75% <0.00%> (-1.03%)	⬇️
... and 48 more

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[behlendorf]

It's good to see some additional zdb test coverage!