refactor(sdk): release lock after discovery complete

[chr1shung]

Add a wrapper function to call discovery.Discovery() and release the
lock when call completed so that developer will not be forced to push
something to deviceCh to release the lock

Signed-off-by: Chris Hung chris@iotechsys.com

PR Checklist

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• The commit message follows our guidelines: https://wiki.edgexfoundry.org/display/FA/Committing+Code+Guidelines#CommittingCodeGuidelines-CommitMessages
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

Issue Number:
fix #609

[codecov-io]

Codecov Report

Merging #624 into master will increase coverage by 0.33%.
The diff coverage is 43.09%.

@@            Coverage Diff             @@
##           master     #624      +/-   ##
==========================================
+ Coverage   53.58%   53.91%   +0.33%     
==========================================
  Files          24       23       -1     
  Lines        2831     2552     -279     
==========================================
- Hits         1517     1376     -141     
+ Misses       1198     1063     -135     
+ Partials      116      113       -3     

Impacted Files	Coverage Δ
internal/autoevent/manager.go	0.00% <0.00%> (ø)
internal/cache/devices.go	96.96% <ø> (+1.78%)	⬆️
internal/cache/provisionwatchers.go	95.45% <ø> (+2.68%)	⬆️
internal/cache/valuedescriptors.go	100.00% <ø> (+3.12%)	⬆️
internal/common/config.go	0.00% <0.00%> (ø)
internal/common/types.go	0.00% <0.00%> (ø)
internal/common/utils.go	17.00% <0.00%> (-2.18%)	⬇️
internal/handler/control.go	0.00% <0.00%> (ø)
internal/transformer/transformparam.go	0.00% <0.00%> (ø)
internal/clients/init.go	8.33% <5.33%> (+1.03%)	⬆️
... and 25 more

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[cloudxxx8]

LGTM