Periodic HeartBeat to be logged to the file

[vrdmr]

Description

Adding Heartbeat logs to file. It logs every 12 hours currently, and helps in debugging.

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

❗ No coverage uploaded for pull request base (develop@5335ef4). Click here to learn what that means.
The diff coverage is 76.31%.

@@            Coverage Diff             @@
##             develop    #1755   +/-   ##
==========================================
  Coverage           ?   69.18%           
==========================================
  Files              ?       82           
  Lines              ?    11720           
  Branches           ?     1644           
==========================================
  Hits               ?     8108           
  Misses             ?     3261           
  Partials           ?      351

Impacted Files	Coverage Δ
azurelinuxagent/daemon/main.py	73.68% <0%> (ø)
azurelinuxagent/common/protocol/util.py	83.41% <0%> (ø)
azurelinuxagent/ga/monitor.py	93.91% <100%> (ø)
azurelinuxagent/ga/remoteaccess.py	88.88% <100%> (ø)
azurelinuxagent/ga/env.py	72.89% <100%> (ø)
azurelinuxagent/ga/update.py	88.76% <100%> (ø)
azurelinuxagent/common/protocol/hostplugin.py	84.15% <100%> (ø)
azurelinuxagent/common/rdma.py	16.84% <33.33%> (ø)
azurelinuxagent/common/protocol/wire.py	77.83% <72.94%> (ø)

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[larohra]

Some minor comments