WIP: Pass mattermost onto Test::Integration::Mattermost
If gitlab-ce!15127 is merged, we need to give the Test::Integration::Mattermost user scenario the address of the mattermost server to check against, we do that via the MATTERMOST_URL environment variable.
This takes the number of arguments for Component::Specs#test_address to 6 from 5, rubocop warns at >5, so add an exception.
Alternate implementation as discussed in !86 (merged)