Some tests were hanging due to the addresses generated by
factory.Faker('ipv4', network=True)

Replace it by a Sequence of /24 addresses

Factory boy doesn't reset the sequence between tests.
We use a sequence to generate unique IP addresses in the InterfaceFactory.
When the sequence number gets too high, the IP is not in the network
range anymore.

To fix the issue, we reset the sequence number when initializing a new
session.

Allow to filter by domains

Not everyone at ICS is part of the 'ICS Employees' AD group.
We have to accept 'ICS Consultants' as well.

The CSENTRY_LDAP_GROUPS settings now takes a list of groups instead of
just one.

Remove unused is_member_of_all_groups method.

Fixes INFRA-225

- add domain_id on NetworkScope table to define a default domain
- add domain_id on Network (default to the Network Scope one)

Fixes INFRA-194

+ fix tests

- refactor Network class

- catch IntegrityError on patch
- disable autoflush (IntegrityError was raised before commit due to
autoflush)

- use same postgres container for dev and test
  (create 2 different databases)
- use docker-compose.override.yml to avoid duplication
- ignore more files not needed in the docker image

By default docker-compose reads both docker-compose.yml and
docker-compose.override.yml.
In docker-compose.override.yml we mount the current directory as
a volume for development.

To test the image we only use docker-compose.yml:
- don't force port 5432 to the outside world to avoid conflict
- do not mount the current directory

Put under the functional directory all tests that require
access to the database. There is a "session" fixture in that
directory that is automatically invoked for each tests. It rollbacks
any transaction after the test to leave the database clean.

Other tests should go under the unit directory.

Inspired from:
- https://stackoverflow.com/a/38626139
- http://alexmic.net/flask-sqlalchemy-pytest/