Set log time format

[larohra]

Description

datetime.isoformat() skips ms if ms=0, this PR replaces using isoformat with a specific ISO 8601 format that always include micro seconds.

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.

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This change is 

[codecov]

Codecov Report

Merging #1737 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           develop    #1737   +/-   ##
========================================
  Coverage    68.21%   68.21%           
========================================
  Files           80       80           
  Lines        11617    11617           
  Branches      1635     1635           
========================================
  Hits          7924     7924           
  Misses        3356     3356           
  Partials       337      337

Impacted Files	Coverage Δ
azurelinuxagent/common/logger.py	93.86% <100%> (ø)	⬆️

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