OS.EnableFirewall=n does not take effect when restarting waagent

If you change `OS.EnableFirewall=y` to `OS.EnableFirewall=n` and restart *waagent* it does not remove the security rules.
One could expect the *waagent* to remove the security rules so that the firewall rules match the setting in */etc/waagent.conf*

Start by tracing waagent's restart handling and how it reads OS.EnableFirewall from /etc/waagent.conf. Reproduce the change from y to n, then verify whether the existing security rules remain after restarting waagent. Done means the rules match the configured setting after restart.

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