update error message if imported webapp belongs to another user

(now that allgo supports multiple e-mail addresses per user, they
 can resolve the problem without the admins)
1 job for qualif in 1 minute and 7 seconds (queued for 2 seconds)
Status Name Job ID Coverage
failed bootstrap #224676


Name Stage Failure
bootstrap Build
Step 7/7 : EXPOSE	25  143
---> Using cache
---> cacb460e7164
Successfully built cacb460e7164
Successfully tagged allgo_dev-smtpsink:latest
+ mkdir -p -- data/mysql
+ docker-compose run --rm dev-mysql sh -e -c 'if [ -f /dk/container_init ] ; then sleep 1; /dk/container_init ; fi'
error: db is already initialised
ERROR: Job failed: exit code 1