922825: pre_subscribe conduit now contains more data

Data added:
- pool_id: the id of the pool from which the entitlement(s) will be consumed
- quantity: the quantity requested to consume

Created seperated slots/conduits for auto-attach
- auto-attach/healing now call pre_auto_attach and post_auto_attach
  hooks.
Merge pull request #622 from candlepin/mstead/more_data_in_pre_subscribe_conduit

922825: pre_subscribe conduit now contains more data