Thread interface

[larohra]

Description

A new interface for all threads to follow in the Guest Agent

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.
• Except for special cases involving multiple contributors, the PR is started from a fork of the main repository, not a branch.
• If applicable, the PR references the bug/issue that it fixes in the description.
• New Unit tests were added for the changes made and Travis.CI is passing.

Quality of Code and Contribution Guidelines

• I have read the contribution guidelines.

[codecov]

Codecov Report

Merging #1990 into develop will decrease coverage by 0.00%.
The diff coverage is 75.00%.

@@             Coverage Diff             @@
##           develop    #1990      +/-   ##
===========================================
- Coverage    71.13%   71.13%   -0.01%     
===========================================
  Files           86       87       +1     
  Lines        12286    12300      +14     
  Branches      1730     1730              
===========================================
+ Hits          8740     8749       +9     
- Misses        3160     3165       +5     
  Partials       386      386              

Impacted Files	Coverage Δ
azurelinuxagent/common/interfaces.py	58.33% <58.33%> (ø)
azurelinuxagent/ga/env.py	65.28% <100.00%> (+0.28%)	⬆️
azurelinuxagent/ga/extension_telemetry.py	91.94% <100.00%> (+0.03%)	⬆️
azurelinuxagent/ga/monitor.py	78.45% <100.00%> (ø)

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