Specify mattermost should use its own suite

The Test::Instance::Mattermost suite doesn't exist yet, but when it does
I expect it will:

* Run all current tests from Test::Instance
* Run additional tests to verify the embedded Mattermost
8 jobs for 26-get-mattermost-running in 15 minutes and 6 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Check
passed #35847799
docker
check:rspec

00:00:54

passed #35847798
docker
check:rubocop

00:00:54

 
  Test
passed #35847802
docker
ce:image

00:07:51

passed #35847800
docker
ce:instance

00:07:07

failed #35847804
docker
ce:upgrade

00:10:11

passed #35847803
docker
ee:image

00:05:18

passed #35847801
docker
ee:instance

00:07:32

failed #35847805
docker
ee:upgrade

00:14:07

 
Name Stage Failure
failed
ee:upgrade Test There is an unknown failure, please try again
rspec ./qa/specs/features/repository/push_spec.rb:4 # push code to repository with regular account over http user pushes code to the repository
rspec ./qa/specs/features/project/create_spec.rb:3 # create a new project user creates a new project

Randomized with seed 7908

Uploading artifacts...
screenshots/*.png: found 5 matching files

Uploading artifacts to coordinator... ok
id=35847805 responseStatus=201 Created token=uyy9zAGs
ERROR: Job failed: exit code 1
failed
ce:upgrade Test There is an unknown failure, please try again
rspec ./qa/specs/features/login/standard_spec.rb:3 # standard root login user logs in using credentials
rspec ./qa/specs/features/project/create_spec.rb:3 # create a new project user creates a new project

Randomized with seed 63806

Uploading artifacts...
screenshots/*.png: found 5 matching files

Uploading artifacts to coordinator... ok
id=35847804 responseStatus=201 Created token=Dt2FRHHS
ERROR: Job failed: exit code 1