lock the rbd volume while importing process #900

Job	Run time
build (3Mi, incr-backup)	34m 11s
build (3Mi, backup-failure)	30m 51s
build (3Mi, change-to-primary)	28m 12s
build (3Mi, full-backup)	28m 21s
build (3Mi, change-to-secondary)	26m 44s
build (3Mi, change-to-standalone)	23m 0s
build (10Mi, various-transfer-part-size)	20m 34s
build (3Mi, lock)	22m 39s
build (3Mi, !//)	37m 54s
build (200Gi, various-transfer-part-size)	21m 6s
build (3Mi, incr-backup)	36m 3s
build (3Mi, full-backup)	28m 21s
build (3Mi, change-to-standalone)	23m 0s
build (3Mi, change-to-primary)	28m 12s
build (3Mi, backup-failure)	30m 51s
build (3Mi, lock)	22m 39s
build (200Gi, various-transfer-part-size)	21m 6s
build (3Mi, change-to-secondary)	26m 44s
build (3Mi, !//)	37m 54s
build (10Mi, various-transfer-part-size)	20m 34s
	9h 8m 56s

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