syz-cluster: select nested vm pool by label #17545

Job	Run time
build	3m 16s
aux	4m 32s
arch (presubmit_arch_freebsd)	6m 16s
arch (presubmit_arch_darwin)	3m 38s
arch (presubmit_arch_openbsd)	3m 37s
arch (presubmit_arch_netbsd)	3m 53s
dashboard	2m 4s
arch (presubmit_arch_linux)	10m 21s
arch (presubmit_arch_windows)	3m 24s
race	9m 48s
race_dashboard	3m 49s
gvisor	3m 55s
arch (presubmit_arch_executor)	3m 16s
old	6m 58s
	1h 8m 47s

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