backups: Create an offsite pool

Introduce an off site pool that will be used to have copies of the
bacula jobs on the offsite Storage Daemon

Change-Id: I1e3d95923bb4a0fcac0a4af9ce7d57ad7dd87aa0
backups: Support next pool directive

The Next pool directive is used to indicate the destination of migration
and copy jobs. We did not have support for that, add it

Change-Id: I0f7898e4d655b3dd8def3ed5c9d1547a858910ce
backups: define next_pool for the production pool

Have the production pool send copy and migration jobs to the offsite
pool. Use the new parameter next_pool for this

Change-Id: I0f4fad05aea3dc77849f6aa887d6a7a55423c14d
backups: add offsite job template

A template job for now

Change-Id: I256e0785b0feed0ef989abbc55b465448b414606