Fixed spec/requests/ authentication specs

- Update session_store to use :memory instead of default cookie_store for tests, eliminating the 4K limit that was giving us the 500's.
- Needed to specify HTTP_USER_AGENT for a couple of tests in auth_spec.rb

This fix is needed before enabling spec:requests as part of test:vmdb for the REST API.

@martinpovolny @Fryguy please review.

And the code that's failing should handle nil user agent IMO.  cc
@bmclaughlin
 On Nov 24, 2014 7:23 PM, "Jason Frey" <fryguydev@gmail.com> wrote:

> Ok bad example.  What about unexpected user agents like "lynx" or "ruby"?
>  On Nov 24, 2014 7:08 PM, "Alberto Bellotti" <notifications@github.com>
> wrote:
>
>> In vmdb/spec/requests/auth_spec.rb:
>>
>> > @@ -39,13 +39,13 @@
>> >    context 'w/ a valid session' do
>> >      it "allows access w/ a valid referer" do
>> >        post '/dashboard/authenticate', :user_name => 'admin', :user_password => 'smartvm'
>> > -      get '/ems_cloud/show_list', nil, 'HTTP_REFERER' => "http://www.example.com/"
>> > +      get '/ems_cloud/show_list', nil, 'HTTP_USER_AGENT' => "chrome", 'HTTP_REFERER' => "http://www.example.com/"
>>
>> REST API authentication is via /api, not the above. For the above,
>> without HTTP_USER_AGENT, I was getting an undefined method downcase for nil
>> for ie8_referer_exception?
>> allowed_access->referer_valid->ie8_referer_exception?
>>
>> —
>> Reply to this email directly or view it on GitHub
>> <https://github.com/ManageIQ/manageiq/pull/1116/files#r20833565>.
>>
>