Before this change, backup backend was initialized twice - in on_init()
and get_backend() functions. This change leaves only one call in
get_backend() and adds a kwarg determining whether init failure should
be fatal.
Signed-off-by: Michal Rostecki <mrostecki@mailfence.com>
We heavily rely on foreign key constraints to keep the DB consistent and drop
dependent objects such as UTXO set entries when we roll back a block. We also
need to enable the foreign key constraints when restoring otherwise these
dependents are not removed and we run into constraint violations.
