test-kpartx: improve step descriptions to ease debugging #494

Job	Run time
build-old (debian-trixie, ppc64le)	47s
build-old (debian-buster, 386)	47s
build-old (debian-buster, arm/v7)	46s
build-old (debian-bookworm, ppc64le)	47s
build-old (ubuntu-trusty, 386)	47s
build-old (debian-trixie, arm/v7)	46s
build-old (ubuntu-trusty, arm/v7)	46s
build-old (debian-bookworm, s390x)	47s
build-old (debian-bookworm, 386)	1s
build-old (debian-trixie, s390x)	47s
build-old (debian-trixie, 386)	46s
build-old (debian-bookworm, arm/v7)	1s
	7m 48s

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