Celery will delete SINGLETONLOCK key when running task

[raven_cc]

Environment:
celery==4.1.0
celery-singleton==0.1.3
redis==2.10.6

Celery will delete SINGLETONLOCK key when running task, adding a 'celery' prefix to the key will fix the issue.
I think using a separate redis backend will be better.

[Steinthor Palsson]

Hey, reopening this to remind me to make the key prefix and redis server URL configurable.