Merge pull request #17 from Jimdo/check_elasticache_status

Only return ElastiCache resources that are available
Refactor elasticache tests

In order to cleanup some messy test codebase and to have a more
real-world-like setup, provide elasticache tests with a proper fixture set.
Merge pull request #19 from Jimdo/refactor_elasticache_tests

Refactor elasticache tests
add failing test for two replication groups
make time values more explicit