cyclades: Update subnets.py to support slac

IPv6 subnets now support a boolean attribute called slac.
If a request for a subnet contains both a slac field and an enable_dhcp
field, only the slac one will be used. If no slac field is found for an
IPv6 subnet, the field enable_dhcp will be used instead.

IPv4 subnets silently ignore any slac field if present and only use
enable_dhcp.

This commit adds the relevant tests in tests/subnets.py too.
cyclades: Refactor backend code for new networks

* Optimize DB queries by using prefetch related for NIC IPs.
* Do not try to construct new NIC if it does not exist in Cyclades DB.
* Update tests
cyclades: Fix some network management commands

* Fix network-list to properly display networks. Add optionally
  'subnets' fields to display the IDs of all subnets
* Fix network-modify to externally reserve the IPs in DB
* Fix network-create to not require a name and subnet4 or subnet6
  options.
cyclades: Add logic ports.py

Created a new file for ports in logic directory. This will have
the code about port manipulation in the backend. For now it is just
used for db filling.
Use the new function 'create' in the ports API.
cyclades: snf-manage port-create

* Create new command snf-manage port-create
* Create new function util.get_security_group
Merge branch 'feature-apidocs-personality-inject' into develop
Merge branch 'develop' of https://code.grnet.gr/git/synnefo into develop
astakos: pep8 fixes
cyclades: Add snf-manage port-remove command
cyclades: Add snf-manage port-inspect command

This command will provide info about the port concerning the DB and
the Ganeti state. For now, it provides only DB info.
cyclades: Various fixes in api/subnets.py
cyclades: Fully support ip pools in subnets
cyclades: Fix a typo in api/subnets.py
astakos: Update docs

Remove obsolete ``usage`` parameter from ``authenticate`` api call
cyclades: s/slac/enable_slac in api/subnets.py
cyclades: Update subnet tests
pithos: Delete rejected quotaholder serials
cyclades: Hack-ish commit for old IP pools
cyclades: PEP8 fixes
cyclades: Fix bug when creating networks