Add ability to use live_server fixture without DB setup

[kottenator]

I have a Django project that cannot have DB - that's a requirement.
When I create a test that uses live_server fixture, I get an error:

ImproperlyConfigured: settings.DATABASES is improperly configured

It seems that you automatically enforce to use DB with live_server fixture. Could you, please, provide a choice for this?

[pelme]

Good idea! If you are interested in this, please send a PR.

I think this should be configured via a marker or so:

@pytest.mark.live_server(database=False)
def test_something(live_server):
    pass

[blueyed]

@kottenator
I wondered myself the other day if it makes sense really to enforce transactional_db with live_server automatically.

As this issue shows there is a use case, and maybe even for using it with db (instead of transactional_db even).

Do you feel like creating a PR for it?