statistic
Fixes: #11189
This introduces a new parameter and makes an existing parameter from
`required` to `optional` as both cannot be specified together
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSCloudWatchMetricAlarm_' 2 ↵ ✹ ✭
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/01/13 11:25:24 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSCloudWatchMetricAlarm_ -timeout 120m
=== RUN TestAccAWSCloudWatchMetricAlarm_importBasic
--- PASS: TestAccAWSCloudWatchMetricAlarm_importBasic (19.80s)
=== RUN TestAccAWSCloudWatchMetricAlarm_basic
--- PASS: TestAccAWSCloudWatchMetricAlarm_basic (20.42s)
=== RUN TestAccAWSCloudWatchMetricAlarm_extendedStatistic
--- PASS: TestAccAWSCloudWatchMetricAlarm_extendedStatistic (18.92s)
PASS
```
8e4f19918a