Enable pragma foreign key for sqlite

Without this pragma, things like CASCADE won't work in sqlite.

Implements blueprint: sql-storage-driver

Change-Id: Ic24036b4b5105d1bf4e70cbf735d85a02fa2dc9a
Fix message's get and deletion

The message get was not returning the expected result. Also,
bulk_message deletion was not deleting messages due to a wrong
serialization of messages ids.

Implements blueprint: sql-storage-driver

Change-Id: I9d04dc9f615b4b1d408a710cc447cfc2ed098286
Register sqlalchemy endpoints

Sqlalchemy endpoints were missing in the setup.cfg entry_points list.

Implements blueprint: sql-storage-driver

Change-Id: I11b77e8c64fc9cb9e027799c7fb015e25e118c56
Don't raise `DoesNotExist` on claims deletion

We don't raise DoesNotExist when the queue that a claim has to be
deleted from does not exist.

Implements blueprint: sql-storage-driver

Change-Id: I2a3e11d493b066c5dae7af81db81989468e90726