Disable custom service

[larohra]

Description

Do not setup agent network service if Os.EnableFirewall = False

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 #2166 (c9a455d) into release-2.2.54 (84bbfbc) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@                Coverage Diff                 @@
##           release-2.2.54    #2166      +/-   ##
==================================================
- Coverage           70.79%   70.77%   -0.03%     
==================================================
  Files                  96       96              
  Lines               13376    13379       +3     
  Branches             1877     1878       +1     
==================================================
- Hits                 9470     9469       -1     
- Misses               3493     3500       +7     
+ Partials              413      410       -3     

Impacted Files	Coverage Δ
azurelinuxagent/ga/update.py	88.38% <100.00%> (-0.10%)	⬇️
azurelinuxagent/common/persist_firewall_rules.py	76.15% <0.00%> (-4.62%)	⬇️
azurelinuxagent/common/conf.py	78.92% <0.00%> (+0.49%)	⬆️
azurelinuxagent/ga/env.py	68.59% <0.00%> (+1.65%)	⬆️

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