correct _sync_instance_power_state log message

As reported by a user: the src and dest hosts listed were actually in
reverse order, making this log message quite confusing to
operators. Flipped to the correct requested order.

Change-Id: If9b31bceb56b66af70cddb88dbece7a180e4c2c8
Closes-Bug: #1370885
Merge "correct _sync_instance_power_state log message"