Create a NativeFilesystem implementation of ReadWriteFilesystem #69

Job	Run time
build-installer-iso-job	2m 46s
test-iso-multidisk-qemu-disk5-with-data-job	2h 13m 6s
test-iso-multidisk-qemu-disk2-with-data-job	2h 12m 20s
test-iso-multidisk-qemu-empty-disk-job	2h 11m 18s
test-iso-qemu-job	2h 3m 0s
test-iso-cf-qemu-job	2h 1m 54s
	10h 44m 24s

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