Comment 7 for bug 1731063

Can see that the Instance object has the key_data when nova-compute boots it:
key_data='ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC9H4ad2IV712wZm5wCgFQPGVEiF9GG1OooX3BXAvEKdhP1vYAq687kOiKV+RmK4qhYiCyp4GF/hKrL4eRmJlSS74AfkvU2w83nqYS97njw5J9mBSeZWzQ4KaHXpVgD7rKtRCoEtufK/WT79sdocSXstQshyWG2w1rAZoaGKOiS1wCHOvV8JkZ45BoVrgiS734bds0MrHxo4r+6nN5WMvAzoLnwJ1Njzyz2b/IWiQfRCljha9F2bLrA9iXTppR2E8HMr+pAH2yFWT/wF6kq8c8vMF/NEFoCuV0ZkIH7ZjLPRFr8I6DiaPeGFVu4Zx1W9PhQsdh3gtyOGswP0MhvYqyJ Generated-by-Nova'
key_name='tempest-TestVolumeBootPattern-1512872222'

And the ip is 10.100.0.4:
"ips": [{"meta": {}, "version": 4, "type": "fixed", "floating_ips": [], "address": "10.100.0.4"}]

However the 404 for the public_key metadata is from 10.100.0.6:
http://logs.openstack.org/79/516979/2/gate/legacy-tripleo-ci-centos-7-scenario001-multinode-oooq-container/13841da/logs/subnode-2/var/log/containers/nova/nova-api-metadata.log.txt.gz#_2017-11-08_21_14_37_476

Which is a different VM that doesn't have a key_pair:
http://logs.openstack.org/79/516979/2/gate/legacy-tripleo-ci-centos-7-scenario001-multinode-oooq-container/13841da/logs/subnode-2/var/log/containers/nova/nova-compute.log.txt.gz#_2017-11-08_21_14_16_781

This looks more like a storage or network issue causing cloud-init to fail on the cirros VM, not an nova metadata issue.