./config.cmd in InstallVstsAgent.ps1 do not work with proxy enabled for a domain joined VM

### Issue Details

Issue related to file : https://github.com/Azure/azure-quickstart-templates/blob/master/201-vm-vsts-agent/scripts/InstallVstsAgent.ps1

InstallVstsAgent.ps1 has ./config.cmd which works perfectly when 'Proxy' is not in place for a VM

### Scenario where it fails:
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We have domain joined Azure VMs which need proxy so that the agent requests can go and talk to internet. We are able to download the agent.zip and extract, but even after mentioning the Proxy url in environment via DSC script the "./config.cmd" script fails to take the default proxy from IE browser or from local account and talk to to VSTS.

### Repro steps
Scenario when ".config.cmd" works :
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1) When i log in through Azure VM serial Console with local account(by resetting password) at portal
2) And when i visit to below url c:\VSTSAgent and run config.cmd , then it configures and even without giving -proxyurl , its able to connect to VSTS/devops

Need an urgent help, where we are going wrong or is this proxy scenario is still not supported ?

Thanks in Advance !

Regards,
Girish Kalamati
Do tweet me at: @TheAzureGuy007

Start with 201-vm-vsts-agent/scripts/InstallVstsAgent.ps1 and inspect how it invokes ./config.cmd after downloading and extracting the agent. Reproduce the failure on a domain-joined Azure VM with a proxy configured through the environment or IE; done means config.cmd can connect to VSTS/DevOps without requiring an explicit proxy URL.

Written by the indexing model from the issue text.