Persist registry in bosh pg db to benefit from bosh backups

[gberche-orange]

Currently, the registry (storing association of bosh id to cloudstack ids: vms, disks) is stored in a local db stored in /vcap/store persistent FS.

As a result, the usual backup of the bosh db would not backup the bosh registry. Loss of the bosh director persistent disk would require recreating the registry, e.g. by recreating all vms and volumes in a bosh deployment.