Merge pull request #169 from cybozu-go/remove-backup-duration-seconds… #830

Job	Run time
build (3Mi, full-backup)	28m 8s
build (3Mi, incr-backup)	31m 21s
build (3Mi, change-to-primary)	28m 20s
build (3Mi, backup-failure)	29m 14s
build (3Mi, change-to-secondary)	26m 56s
build (10Mi, various-transfer-part-size)	20m 9s
build (3Mi, change-to-standalone)	21m 8s
build (200Gi, various-transfer-part-size)	20m 8s
build (3Mi, !//)	36m 15s
	4h 1m 39s

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