Fix incorrect liquibase references to instance_id

[kahowell]

Confusingly, we have a column named instance_id on the hosts table;
we also have a column named instance_id on instance_measurements.
However, the instance_id on instance_measurements references
hosts.id and NOT hosts.instance_id.

Testing

Try the following sql for testing the trigger change:

insert into account_services(account_number, service_type) values ('a123', 'HBI_HOST');
insert into hosts(id, instance_id, display_name, account_number, org_id, cores, sockets)
values ('0cfbdd0e-8f5d-4152-9945-f8fd452c2b2d', 'foobar', 'foo', 'a123', 'org123', 4, null);
select * from instance_measurements;

The original testing instructions used the same value for both id and
instance_id, which is possibly why this wasn't caught sooner.

Note that given the changesets involved were modified, I added
runOnChange=true to simplify re-running against deployments where it's
already run.