Make installing the guest agent configurable
Make installing the guest agent configurable

I know this would probably go into an option struct, but I think that
should be another refactor. So for now just added a `bool`.

And while touching this file I also made it’s 100+ lines a little
shorter which makes reviewing on GH a lot nicer.

curoverse/azure-sdk-for-go,colemickens/azure-sdk-for-go,lirao/azure-sdk-for-go,oaastest/azure-sdk-for-go,kenegozi/azure-sdk-for-go,MindFlavor/azure-sdk-for-go,Azure/azure-sdk-for-go,Nepomuceno/azure-sdk-for-go,Nepomuceno/azure-sdk-for-go,kenegozi/azure-sdk-for-go,Azure/azure-sdk-for-go,paulmey/azure-sdk-for-go,mvanotti/azure-sdk-for-go,Nepomuceno/azure-sdk-for-go,marstr/azure-sdk-for-go,bingosummer/azure-sdk-for-go,marstr/azure-sdk-for-go,mvanotti/azure-sdk-for-go,stubey/azure-sdk-for-go,mvanotti/azure-sdk-for-go,aznashwan/azure-sdk-for-go,aznashwan/azure-sdk-for-go,oaastest/azure-sdk-for-go,paulmey/azure-sdk-for-go,lirao/azure-sdk-for-go,oaastest/azure-sdk-for-go,marstr/azure-sdk-for-go,curoverse/azure-sdk-for-go,Azure/azure-sdk-for-go,MindFlavor/azure-sdk-for-go,StorReduce/azure-sdk-for-go,StorReduce/azure-sdk-for-go,StorReduce/azure-sdk-for-go,garimakhulbe/azure-sdk-for-go,kenegozi/azure-sdk-for-go,MindFlavor/azure-sdk-for-go,Azure/azure-sdk-for-go,paulmey/azure-sdk-for-go,bingosummer/azure-sdk-for-go,stubey/azure-sdk-for-go,bingosummer/azure-sdk-for-go,aznashwan/azure-sdk-for-go