Add proxy support in kvm

- Add proxy option to "kvm upgrade"
- "kvm upgrade" uses global proxy (http_proxy env var) by default
- Support authenticated proxies
Added simplified kvm install instructions for OSX/Linux
Merge pull request #86 from graemechristie/update-getting-started-for-kvminstall-sh

Update Getting Started section with kvminstall.sh details
Fixed reference to kvmsetup.sh to reference kvminstall.sh
Fixed sample output for windowsgetting started to show kvm setup command rather than erroneous kvmsetup
Merge pull request #87 from graemechristie/patch-1

Fix reference to kvmsetup.sh to reference kvminstall.sh
Updated kvm to the latest versions
Merge pull request #1 from aspnet/master

Syncing from upstream