Make kubectl proxy accept empty path

The proxy previously returned 403 Forbidden: Unauthorized when receiving a request from e.g. "curl localhost:8001" or "curl localhost:8001/".  The previous DefaultPathAcceptRE regex was wrong as it assumed the path in this case would be "/" (but it is actually "").

pkg/kubectl/proxy_server.go

@@ -34,7 +34,7 @@ import (
 
 const (
 	DefaultHostAcceptRE   = "^localhost$,^127\\.0\\.0\\.1$,^\\[::1\\]$"
-	DefaultPathAcceptRE   = "^/.*"
+	DefaultPathAcceptRE   = "^.*"
 	DefaultPathRejectRE   = "^/api/.*/pods/.*/exec,^/api/.*/pods/.*/attach"
 	DefaultMethodRejectRE = "POST,PUT,PATCH"
 )