Allow Static IP for the temporarily machine

Hello,
This issue doesn't need long description, as even the titles says it enough.
The temp VM at the moment is assigned temporarily dynamic IP, however we have a good security, and we cannot allow our environment to access random public IPs, so we need to put the IP we want to access in the firewall.

At the moment, packer and azure is simply not working for us except if we introduce another proxy after our proxy to make this work.
I tried to introduce a PR, which will allow assigning a static ip parameter, but I'm not so good with GO.

If no one has time to do it, I would be happy to reach to someone and perhaps he can give me some heads up, what I must change to make this work as a separate parameter - PublicStaticIP - "x.x.x.x"

The issue names no files or tests; begin by tracing how the Azure plugin provisions the temporary VM and assigns its public IP. Done means a PublicStaticIP parameter can be supplied and the temporary machine uses that address instead of a randomly assigned dynamic IP.

Written by the indexing model from the issue text.