Be more exact when detecting IMDS service health

[ghost]

Description

This change removes the fault from IMDS when connection errors and throttling occurs.

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PR information

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• 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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This change is 

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (develop@b82a31b). Click here to learn what that means.
The diff coverage is 95.34%.

@@            Coverage Diff             @@
##             develop    #1695   +/-   ##
==========================================
  Coverage           ?   67.62%           
==========================================
  Files              ?       80           
  Lines              ?    11498           
  Branches           ?     1613           
==========================================
  Hits               ?     7775           
  Misses             ?     3381           
  Partials           ?      342

Impacted Files	Coverage Δ
azurelinuxagent/common/protocol/imds.py	95.39% <95.34%> (ø)

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[vrdmr]

Minor comments.

[narrieta]

LGTM; will merge once the other comments are addressed.

[pgombar]

LGTM, minor comments.

[vrdmr]

Minor. LGTM.