…ntifiers

This also switches some of the hardcoded us-west-2 testing to use the aws_availability_zones data source so the testing is more region agnostic. Now its at least possible to run parallel testing locally in us-east-1 of an EC2-Classic enabled AWS account.

References:

- #9906
- #9131
- #7409
- #5381

Output from acceptance testing:

```
--- PASS: TestAccAWSElasticacheCluster_AZMode_Memcached_Ec2Classic (515.21s)
--- PASS: TestAccAWSElasticacheCluster_AZMode_Redis_Ec2Classic (507.64s)
--- PASS: TestAccAWSElasticacheCluster_Engine_Memcached_Ec2Classic (663.59s)
--- PASS: TestAccAWSElasticacheCluster_Engine_Redis_Ec2Classic (595.65s)
--- PASS: TestAccAWSElasticacheCluster_EngineVersion_Memcached_Ec2Classic (1260.72s)
--- PASS: TestAccAWSElasticacheCluster_EngineVersion_Redis_Ec2Classic (1303.63s)
--- PASS: TestAccAWSElasticacheCluster_multiAZInVpc (737.16s)
--- PASS: TestAccAWSElasticacheCluster_NodeTypeResize_Memcached_Ec2Classic (954.44s)
--- PASS: TestAccAWSElasticacheCluster_NodeTypeResize_Redis_Ec2Classic (1022.11s)
--- PASS: TestAccAWSElasticacheCluster_NumCacheNodes_Decrease (995.54s)
--- PASS: TestAccAWSElasticacheCluster_NumCacheNodes_Increase (1038.00s)
--- PASS: TestAccAWSElasticacheCluster_NumCacheNodes_IncreaseWithPreferredAvailabilityZones (958.56s)
--- PASS: TestAccAWSElasticacheCluster_NumCacheNodes_Redis_Ec2Classic (6.63s)
--- PASS: TestAccAWSElasticacheCluster_ParameterGroupName_Default (596.16s)
--- PASS: TestAccAWSElasticacheCluster_Port_Ec2Classic (576.63s)
--- PASS: TestAccAWSElasticacheCluster_ReplicationGroupID_AvailabilityZone_Ec2Classic (1214.33s)
--- PASS: TestAccAWSElasticacheCluster_ReplicationGroupID_InvalidAttributes (8.37s)
--- PASS: TestAccAWSElasticacheCluster_ReplicationGroupID_MultipleReplica_Ec2Classic (1884.91s)
--- PASS: TestAccAWSElasticacheCluster_ReplicationGroupID_SingleReplica_Ec2Classic (1746.94s)
--- PASS: TestAccAWSElasticacheCluster_SecurityGroup (626.97s)
--- PASS: TestAccAWSElasticacheCluster_snapshotsWithUpdates (1167.22s)
--- PASS: TestAccAWSElasticacheCluster_vpc (646.18s)
--- PASS: TestAccAWSElasticacheReplicationGroup_basic (1857.56s)
--- PASS: TestAccAWSElasticacheReplicationGroup_clusteringAndCacheNodesCausesError (10.99s)
--- PASS: TestAccAWSElasticacheReplicationGroup_ClusterMode_Basic (1875.48s)
--- PASS: TestAccAWSElasticacheReplicationGroup_ClusterMode_NumNodeGroups (3713.74s)
--- PASS: TestAccAWSElasticacheReplicationGroup_enableAtRestEncryption (1419.18s)
--- PASS: TestAccAWSElasticacheReplicationGroup_enableAuthTokenTransitEncryption (734.55s)
--- PASS: TestAccAWSElasticacheReplicationGroup_enableSnapshotting (1917.01s)
--- PASS: TestAccAWSElasticacheReplicationGroup_importBasic (806.91s)
--- PASS: TestAccAWSElasticacheReplicationGroup_multiAzInVpc (950.44s)
--- PASS: TestAccAWSElasticacheReplicationGroup_NumberCacheClusters (2821.85s)
--- PASS: TestAccAWSElasticacheReplicationGroup_NumberCacheClusters_Failover_AutoFailoverDisabled (2029.86s)
--- PASS: TestAccAWSElasticacheReplicationGroup_NumberCacheClusters_Failover_AutoFailoverEnabled (1919.87s)
--- PASS: TestAccAWSElasticacheReplicationGroup_redisClusterInVpc2 (737.16s)
--- PASS: TestAccAWSElasticacheReplicationGroup_updateDescription (1240.24s)
--- PASS: TestAccAWSElasticacheReplicationGroup_updateMaintenanceWindow (1047.59s)
--- PASS: TestAccAWSElasticacheReplicationGroup_updateNodeSize (1985.53s)
--- PASS: TestAccAWSElasticacheReplicationGroup_updateParameterGroup (900.33s)
--- PASS: TestAccAWSElasticacheReplicationGroup_Uppercase (594.69s)
--- PASS: TestAccAWSElasticacheReplicationGroup_vpc (1355.75s)
```

…sterId into inline ValidateFunc

Reference: #8424

Output from acceptance testing:

```
--- PASS: TestAccAWSDAXCluster_encryption_disabled (739.98s)
--- PASS: TestAccAWSDAXCluster_basic (756.03s)
--- PASS: TestAccAWSDAXCluster_importBasic (796.86s)
--- PASS: TestAccAWSDAXCluster_encryption_enabled (865.80s)
--- PASS: TestAccAWSDAXCluster_resize (1414.26s)
```