GA Versioning: Download required version if available

[larohra]

Description

PR for GAVersioning -

• If requested version is specified in the GS, download only that
• Purge all other agents from the directory

Issue #

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PR information

• The title of the PR is clear and informative.
• There are a small number of commits, each of which has an informative message. This means that previously merged commits do not appear in the history of the PR. For information on cleaning up the commits in your pull request, see this page.
• If applicable, the PR references the bug/issue that it fixes in the description.
• New Unit tests were added for the changes made

Quality of Code and Contribution Guidelines

• I have read the contribution guidelines.

[codecov]

Codecov Report

Merging #2467 (a9d48c3) into develop (c964d70) will increase coverage by 0.04%.
The diff coverage is 89.28%.

@@             Coverage Diff             @@
##           develop    #2467      +/-   ##
===========================================
+ Coverage    71.96%   72.00%   +0.04%     
===========================================
  Files          101      101              
  Lines        15016    15053      +37     
  Branches      2384     2392       +8     
===========================================
+ Hits         10806    10839      +33     
- Misses        3726     3732       +6     
+ Partials       484      482       -2     

Impacted Files	Coverage Δ
azurelinuxagent/ga/update.py	88.80% <89.28%> (-0.10%)	⬇️
azurelinuxagent/common/event.py	85.36% <0.00%> (-0.68%)	⬇️
azurelinuxagent/ga/exthandlers.py	85.90% <0.00%> (+0.14%)	⬆️
azurelinuxagent/ga/collect_telemetry_events.py	90.41% <0.00%> (+0.68%)	⬆️

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