Install Bazel into Ubuntu base images #124

Job	Run time
build-manylinux-builder-images (7.2.0)	26s
build-manylinux-builder-images (7.1.1)	8s
build-base-images (7.2.0, false)	11m 49s
build-base-images (7.1.1, false)	10m 0s
build-base-images (7.2.0, true)	12m 33s
build-base-images (7.1.1, true)	11m 38s
build-manylinux-builder-images (7.1.1)	17m 33s
build-manylinux-builder-images (7.2.0)	26s
build-base-images (7.1.1, true)	11m 38s
build-base-images (7.2.0, true)	12m 33s
build-base-images (7.2.0, false)	11m 49s
build-base-images (7.1.1, false)	10m 0s
build-manylinux-builder-images (7.2.0)	19m 34s
build-base-images (7.1.1, true)	11m 38s
build-manylinux-builder-images (7.1.1)	17m 33s
build-base-images (7.2.0, true)	12m 33s
build-base-images (7.1.1, false)	10m 0s
build-base-images (7.2.0, false)	11m 49s
	3h 13m 40s

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