Update generated prefix for redis instances
Update generated prefix for redis instances

I got confused looking at test output when the database name was test-es
and assumed these were elasticsearch intstances - redis is more
descriptive

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf