Move migration_get_..._by_host_and_node to conductor

This moves the remaining migration-related database call out of the
resource tracker to conductor:

  migration_get_in_progress_by_host_and_node()

Related to blueprint no-db-compute

Change-Id: I9bdf9fbbc3131964bf6078d19bf1cd9053a7e224
Merge "Move migration_get_..._by_host_and_node to conductor"