Update UA string for SDK

[fiveisprime]

I'm not sure if this is the correct repo for this...

The ms-rest module has an method to update the UA String for tracking the origin of requests on the server side. We need to set this for the extensions so we can log requests from VS Code.

client.addUserAgentInfo(`vscode-${package.name}/${package.version}`)

[ejizba]

Closing this as we now have individual issues in each repo.