Convert remaining *_id columns to 64 bit

Note: Performing a change_column on a column with an index is expensive, so
we drop the index if it exists beforehand and add it back unconditionally after.
The latter also fixes the *_id columns missing indexes, such as cloud_volumes.

How to locate 32 bit *_id columns:
  `grep -En "create_table|integer.+_id\b" db/schema.rb | grep -v ":limit => 8"`

Modeled after: db/migrate/20100621174417_convert_ids_to64bit.rb