Recently this change [1] in glance-manage db_sync is internally
using Expand, Migrate and Contract. EMC is explicitly used for
online migration for which glance uses triggers to sync data
between old columns and new columns. DB Sync is used for
offline migartion for which adding triggers is not required.
Made provision to execute triggers explicitly in case of
online migration (EMC pattern) and skip the same in
case of offline migration (db sync).
[1] https://review.openstack.org/#/c/433934/
Closes-Bug: #1749640
Change-Id: I816c73405dd61d933182ad5efc24445a0add4eea
14e8a7b53b