etcd always starts even when mounting EBS volume fails

[vroad]

While there are several other minor issues, this one is the most severe.
Mounting and formatting EBS volumes always fails because etcd3-bootstrap is currently not working correctly.
And etcd-member systemd unit does not check if data directory is correctly mounted. Any data should be stored there will be lost once the instance in ASG is replaced.

monzo/etcd3-bootstrap#4
monzo/etcd3-bootstrap#5