feat: hermetic build OS detection #3380

Job	Run time
lint	26s
build(8) except for gapic-generator-java	4m 21s
build (11)	19m 38s
build (17)	16m 5s
compatibility	1m 41s
build(8) for gapic-generator-java	13m 3s
downstream-compatibility (google-cloud-java)	16m 53s
downstream-compatibility (java-bigtable)	2m 50s
downstream-compatibility (java-bigquery)	4m 1s
downstream-compatibility (java-bigquerystorage)	8m 33s
downstream-compatibility (java-datastore)	3m 2s
downstream-compatibility (java-firestore)	2m 22s
downstream-compatibility (java-logging)	2m 6s
downstream-compatibility (java-logging-logback)	1m 39s
downstream-compatibility (java-pubsub)	10m 35s
downstream-compatibility (java-pubsublite)	3m 17s
downstream-compatibility (java-spanner-jdbc)	2m 14s
downstream-compatibility (java-spanner)	5m 1s
downstream-compatibility (java-storage)	3m 41s
downstream-compatibility (java-storage-nio)	2m 50s
gapic-generator-java-bom	2m 19s
requirements-kokoro	1m 21s
showcase-clirr	57s
showcase (11)	5m 22s
showcase (17)	5m 19s
showcase-native	11m 49s
	2h 31m 25s

Provide feedback