testRunner.py exit with representative code

We want our testRunner script to exit with an error code if tests
failed for gitlab-ci
4 jobs for feature-s/server_unit_tests in 31 seconds (queued for 4 seconds)
Name Stage Failure
test_server_unit Test Unit There is an unknown failure, please try again
Database drivers available: sqlite3, imaplib, pymysql, pg8000
18 controller files with possible doctests found.
Run doctests
Makefile:12: recipe for target 'unit' failed
make[1]: *** [unit] Error 1
make[1]: Leaving directory '/home/gitlab-runner/builds/b8d876c1/0/vidjil/vidjil/server'
Makefile:40: recipe for target 'unit_server' failed
make: *** [unit_server] Error 2
ERROR: Job failed: exit status 1