Use globset to specify src for nix-snapshotter #603

Job	Run time
lint (golangci-lint)	5s
build (nix-snapshotter)	38s
build (image-hello)	36s
build (image-redis)	43s
build (image-redisWithShell)	30s
integration-test (snapshotter)	3m 45s
integration-test (push-n-pull)	3m 8s
integration-test (kubernetes)	4m 15s
integration-test (k3s)	12m 0s
integration-test (k3s-external)	13m 9s
integration-test (k3s-rootless)	11m 50s
integration-test (gvisor)	3m 12s
coverage-report	3m 0s
	56m 51s

Provide feedback