Fix for sending wrong header to HostGA /extensionManifest calls

[larohra]

Description

This PR is to fix the bug where we don't send the correct headers for /extensionArtifacts calls made to HostGA.

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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.
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• New Unit tests were added for the changes made and Travis.CI is passing.

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This change is 

[codecov]

Codecov Report

Merging #1510 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           develop    #1510   +/-   ##
========================================
  Coverage    60.88%   60.88%           
========================================
  Files           75       75           
  Lines        10882    10882           
  Branches      1560     1560           
========================================
  Hits          6625     6625           
  Misses        3942     3942           
  Partials       315      315

Impacted Files	Coverage Δ
azurelinuxagent/common/protocol/wire.py	69.12% <100%> (ø)	⬆️

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[larohra]

Reviewable status: 0 of 2 files reviewed, 3 unresolved discussions (waiting on @narrieta and @pgombar)

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tests/protocol/test_wire.py, line 405 at r2 (raw file):

call to client.fetch_
Sounds fair, will make the changes

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tests/protocol/test_wire.py, line 424 at r2 (raw file):

Previously, narrieta (Norberto Arrieta) wrote…

can we add a little more detail to the comments? thanks

Will do, thanks!

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tests/protocol/test_wire.py, line 426 at r2 (raw file):

Previously, narrieta (Norberto Arrieta) wrote…

let's move the call to client.fetch_manifest out of the assert to make it clear who we are testing (AAA unit test pattern). thanks

Done

[pgombar]

Thanks for fixing this, LGTM!

[narrieta]

thanks for the update, LGTM