No need to specify TEST_DATA_PATH env var; consistent location/name for the local cluster configuration. (#4132)
This PR makes integration test suite work without requiring the
environment variable "SHELLEY_TEST_DATA";
On top of it, the naming was made consistent:
**Before:**
"SHELLEY_DATA_PATH", "cardano-node-shelley", "cluster setup dir" etc.
**After:**
- the directory is renamed to
`lib/local-cluster/test/data/cluster-configs`
- the env var is renamed to "LOCAL_CLUSTER_CONFIGS"
- the `Config`'s data type accessor function is `cfgClusterConfigs`