[functional testing] Fix staging CI job on tbb-0.9.0

[redshiftzero]

We removed the application/functional test run from the staging environment in #3697. We should also update the testinfra test references and remove the application test run from CI, otherwise we get a few testinfra test failures due to pip deps, and an error when we attempt to run the application tests in CI:

TASK [Run application tests] ***************************************************
    Friday 10 August 2018  19:28:17 +0000 (0:00:00.037)       0:01:08.223 *********
    fatal: [app-staging]: FAILED! => {"changed": true, "msg": "non-zero return code", "rc": 127, "stderr": "Shared connection to 52.36.194.59 closed.\r\n", "stdout": "/home/sdrop/.ansible/tmp/ansible-tmp-1533929297.62-93522333058246/app-tests.sh: line 13: pytest: command not found\r\n", "stdout_lines": ["/home/sdrop/.ansible/tmp/ansible-tmp-1533929297.62-93522333058246/app-tests.sh: line 13: pytest: command not found"]}
    ...ignoring