The inventory_hostname is more reliable than ansible_hostname for the
way we use it here. If the deploy node cannot resolve the hostname of a
target node (the operator is using IP addresses in their inventory), the
bootstrap will fail with:
"Host: x.x.x.x, Task: ceph : Fetching Ceph keyrings, Status:
unreachable, Message: SSH Error: data could not be sent to the remote
host. Make sure this host can be reached over ssh"
Closes-Bug: 1599138
Change-Id: Ic76e4baf8c642c59bbe81e6671ac97bcbb57d470
a479afac4a