Security group already exists error

When the initialization of the cluster fails for some reason, but the "dask ecs" security group has already been created on following attempts the initialization fails due to the security group already existing. To get around this it is possible look up the id of the security group and give as an argument in cluster initialization.

I think it would be better
a) to look for an existing security group or
b) to delete the security group when failing to initialize the cluster.

I think a) is more robust :)

Greetings