Rename chart to vsts-agent

Don't really need helm- in the name?
make helm-packge requires chart name to be same as chart dir name

charts/vsts-agent/Chart.yaml

@@ -1,5 +1,5 @@
 apiVersion: v1
-name: helm-vsts-agent
+name: vsts-agent
 version: 1.0.0
 description: Helm chart for Visual Studio Team Services agent pool
 maintainers: