sql: deleting policies does not delete associated records with mysql driver

[johnwu96822]

In MySQL there are four tables for ladon policies. When deleting a policy, it is only deleted from "ladon_policy" table, but the data for this policy in three other ladon_policy_* tables are not removed.

[johnwu96822]

This happens on MySQL

[aeneasr]

@johnwu96822 is this a critical issue for you?

[johnwu96822]

@arekkas Yes we have deployed Hydra for testing. If this issue doesn't get fixed and we modify policies (Hydra currently modifies a policy by deleting and recreating it), we'll get a bunch of policy records in those tables and we wouldn't know which record we'd get.

[aeneasr]

see 070520d

[aeneasr]

resolved by #329