add unit tests for edgex client

[wawlian]

What type of PR is this?

/kind enhancement

What this PR does / why we need it:

Add unit tests for edgex client.

Which issue(s) this PR fixes:

Fixes #41

Special notes for your reviewer:

NONE

Does this PR introduce a user-facing change?

NONE

[codecov]

Codecov Report

Merging #56 (7c0efc6) into main (2fa8ab1) will increase coverage by 23.09%.
The diff coverage is 92.98%.

@@             Coverage Diff             @@
##             main      #56       +/-   ##
===========================================
+ Coverage   22.30%   45.40%   +23.09%     
===========================================
  Files          10       14        +4     
  Lines         919     1729      +810     
===========================================
+ Hits          205      785      +580     
- Misses        676      837      +161     
- Partials       38      107       +69     

Impacted Files	Coverage Δ
pkg/clients/edgex-foundry/device_client.go	56.41% <80.95%> (ø)
pkg/clients/edgex-foundry/deviceservice_client.go	56.07% <100.00%> (ø)
pkg/clients/edgex-foundry/util.go	92.10% <100.00%> (ø)
pkg/clients/edgex-foundry/deviceprofile_client.go	56.81% <0.00%> (ø)
pkg/controllers/deviceservice_controller.go	44.11% <0.00%> (+0.73%)	⬆️

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[openyurt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gnunu, lwmqwer, wawlian

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• OWNERS [wawlian]

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[lwmqwer]

/lgtm