Issue #574: Better ssh config for short-lived cert (#763)

This PR is made using suggestion from #574. The pros for this config is that it will work both Windows and Linux (tested), as well as in VSCode, which normally can't be done with the current generated ssh config (refers to #734)

cmd/cloudflared/access/cmd.go

@@ -37,16 +37,13 @@ const (
 	sshConfigTemplate  = `
 Add to your {{.Home}}/.ssh/config:
 
-Host {{.Hostname}}
 {{- if .ShortLivedCerts}}
-  ProxyCommand bash -c '{{.Cloudflared}} access ssh-gen --hostname %h; ssh -tt %r@cfpipe-{{.Hostname}} >&2 <&1'
-
-Host cfpipe-{{.Hostname}}
-  HostName {{.Hostname}}
+Match host {{.Hostname}} exec "{{.Cloudflared}} access ssh-gen --hostname %h"
   ProxyCommand {{.Cloudflared}} access ssh --hostname %h
-  IdentityFile ~/.cloudflared/{{.Hostname}}-cf_key
-  CertificateFile ~/.cloudflared/{{.Hostname}}-cf_key-cert.pub
+  IdentityFile ~/.cloudflared/%h-cf_key
+  CertificateFile ~/.cloudflared/%h-cf_key-cert.pub
 {{- else}}
+Host {{.Hostname}}
   ProxyCommand {{.Cloudflared}} access ssh --hostname %h
 {{end}}
 `