Right now, we only create the ec2_ids for an Instance when they are first
accessed, not at instance creation time. However, we always touch them
later for building metadata, configdrive, etc, which means we end up with
an expensive lazy-load later.
This makes us always create ec2_ids at instance create time. Since it's in
instance.create(), it runs on conductor, straight to the database, avoiding
a round-trip later (assuming this instance is passed to the compute node
for create and/or that the field is specified in a later call under
expected_attrs).
Partial-Bug: #1540526
Change-Id: I29bc317f990bfa0f01b4f9615699debcc3a3c2c6
c5a5a7f322