Use Security Group rules instead of inline rule blocks. Fix example. Fix README. Update to latest versions of modules. Change region for tests

what

Use Security Group rules instead of inline rule blocks
Fix example. Fix README
Update to latest versions of modules
Change region for tests
Add possibility to use existing Security Groups to place the Redis cluster into
Add the possibility to setup cluster_mode https://www.terraform.io/docs/providers/aws/r/elasticache_replication_group.html#cluster_mode

Use Security Group rules instead of inline rule blocks - make the module idempotent
Fix example. Fix README - add working example to the example section in README
Update to latest versions of modules - be up to date
Change region for tests - we use us-east-2 for all test (us-west-1 is a very limited region)
Add possibility to use existing Security Groups to place the Redis cluster into - in case it's not allowed to create SG in the module
Add the possibility to setup cluster_mode - Create a native Redis cluster with shards