Update kubernetes dependencies to v1.17.6

This also locks golang.org/x/sys/unix as it's another transitive dep that
flaps.

internal/lockdeps/lockdeps.go

@@ -5,4 +5,5 @@ import (
 	// This is a dep that `go mod tidy` keeps removing, because it's a transitive dep that's pulled in via a test
 	// See: https://github.com/golang/go/issues/29702
 	_ "github.com/prometheus/client_golang/prometheus"
+	_ "golang.org/x/sys/unix"
 )