Don't rebuild existing protos in oak_containers_launcher #189

Job	Run time
build_attest_all (buildconfigs/key_xor_test_app.sh)	2m 36s
build_attest_all (buildconfigs/oak_client_android_app.sh)	45m 20s
build_attest_all (buildconfigs/oak_containers_kernel.sh)	26m 53s
build_attest_all (buildconfigs/oak_containers_orchestrator.sh)	7m 4s
build_attest_all (buildconfigs/oak_containers_stage1.sh)	4m 6s
build_attest_all (buildconfigs/oak_containers_syslogd.sh)	6m 23s
build_attest_all (buildconfigs/oak_containers_agent.sh)	4m 53s
build_attest_all (buildconfigs/oak_containers_system_image.sh)	12m 51s
build_attest_all (buildconfigs/oak_echo_enclave_app.sh)	2m 39s
build_attest_all (buildconfigs/oak_echo_raw_enclave_app.sh)	2m 31s
build_attest_all (buildconfigs/oak_functions_enclave_app.sh)	2m 38s
build_attest_all (buildconfigs/oak_functions_insecure_enclave_app.sh)	2m 45s
build_attest_all (buildconfigs/oak_orchestrator.sh)	2m 37s
build_attest_all (buildconfigs/oak_restricted_kernel_simple_io_init_rd_wrapper_bin.sh)	3m 10s
build_attest_all (buildconfigs/stage0_bin.sh)	3m 12s
	2h 9m 38s

Provide feedback