Add support for additional subjects in build.yaml. #49

Job	Run time
build_attest_all (buildconfigs/key_xor_test_app.sh)	2m 20s
build_attest_all (buildconfigs/oak_containers_kernel.sh)	11m 12s
build_attest_all (buildconfigs/oak_containers_orchestrator.sh)	6m 23s
build_attest_all (buildconfigs/oak_containers_stage1.sh)	3m 46s
build_attest_all (buildconfigs/oak_containers_syslogd.sh)	5m 58s
build_attest_all (buildconfigs/oak_containers_system_image.sh)	11m 54s
build_attest_all (buildconfigs/oak_echo_enclave_app.sh)	2m 13s
build_attest_all (buildconfigs/oak_echo_raw_enclave_app.sh)	2m 18s
build_attest_all (buildconfigs/oak_functions_enclave_app.sh)	2m 30s
build_attest_all (buildconfigs/oak_functions_insecure_enclave_app.sh)	2m 29s
build_attest_all (buildconfigs/oak_orchestrator.sh)	2m 23s
build_attest_all (buildconfigs/oak_restricted_kernel_simple_io_init_rd_wrapper_bin.sh)	2m 51s
build_attest_all (buildconfigs/stage0_bin.sh)	2m 17s
	58m 34s

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