feat(blockdevicefilter): add filter for empty block device tag label value

[ajeetrai7]

This PR adds a filter that does not select
BD that has empty block device tag value.
Ref: openebs/openebs#3139

Signed-off-by: ajeetrai707 ajeetrai707@gmail.com

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[codecov-io]

Codecov Report

Merging #500 into master will decrease coverage by 4.31%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #500      +/-   ##
==========================================
- Coverage   51.47%   47.15%   -4.32%     
==========================================
  Files          73       73              
  Lines        5076     3274    -1802     
==========================================
- Hits         2613     1544    -1069     
+ Misses       2213     1573     -640     
+ Partials      250      157      -93     

Impacted Files	Coverage Δ
pkg/select/blockdevice/filters.go	17.69% <33.33%> (+0.42%)	⬆️
pkg/udev/listentry.go	0.00% <0.00%> (-59.26%)	⬇️
api-service/node/services/hugepages.go	0.00% <0.00%> (-58.34%)	⬇️
pkg/sysfs/device.go	0.00% <0.00%> (-52.95%)	⬇️
cmd/ndm_daemonset/probe/customtagprobe.go	28.12% <0.00%> (-51.47%)	⬇️
cmd/ndm_daemonset/probe/sysfsprobe.go	0.00% <0.00%> (-48.47%)	⬇️
...m_daemonset/controller/disk_to_device_convertor.go	0.00% <0.00%> (-46.16%)	⬇️
pkg/smart/diskinfo.go	0.00% <0.00%> (-37.15%)	⬇️
cmd/ndm_daemonset/probe/usedbyprobe.go	15.66% <0.00%> (-36.77%)	⬇️
pkg/smart/satadevice.go	0.00% <0.00%> (-28.89%)	⬇️
... and 43 more

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[akhilerm]

@AJEETRAI707 , given a few comments.

[kmova]

Also, is it allowed to pass a BD tag with empty value in BDC.

Shouldn't this be 0? because "" will always be excluded.

[kmova]

cc: @akhilerm

[akhilerm]

Also, is it allowed to pass a BD tag with empty value in BDC.

Yes. it is allowed, because its a valid label selector.

Shouldn't this be 0? because "" will always be excluded.

Actually 2 levels of filtering happens. The original BD List that we get here, will be after a label selection as part of the list call. So those selectors will already be applied. But if those selectors are applied, we still need to remove the empty tag, thats being done in this filter.

So the tests assume that already a selection has happened with the list call. And the output of the tests will be therefore including the BDs that would have been removed by the select call. Thats why the additional 4 BDs come.

[akhilerm]

If you check this comment , you can see how the filter works.