fix(db) fix the 0.14 -> 1.1 migration path for Cassandra
fix(db) fix the 0.14 -> 1.1 migration path for Cassandra

In `kong/db/migrations/core/003_100_to_110.lua`, we added new fields
`tags` and `protocols` to the `plugins` table in the `up` phase, however,
the `plugins` table was recreated in `kong/db/migrations/core/001_14_to_15.lua`'s
`teardown` phase without those two fields. This results green clusters
to throw HTTP 500 error for all proxy requests after `kong migrations
finish` is executed.

Thanks @thibaultcha for helping on determining the fix.

From #4450
Mashape/kong,Kong/kong,Kong/kong,Kong/kong