Trades runtime complexity for spacial complexity when modifying
large amounts of contexts on a kubeconfig.
In cases where there are few destination filenames for a given
amount of contexts, but a large amount of contexts, this patch
prevents reading and writing to the same file (or small number
of files) over and over again needlessly.
Kubernetes-commit: d5651948cf1a14ed284b4708e2057e4cbc72bcbe
