DeploymentPreference Alarms and Fn::If

[keetonian]

I took a look into the Alarm error from #350.

I replicated the reported issue by using an Fn::If intrinsic in the Alarms section of my template:

...
        Alarms:
          Fn::If:
            - IsBetaStage:
            - - { Ref: IncreasedFaults }
              - { Ref: IncreasedLatency }
            - - { Ref: IncreasedFaults2 }
              - { Ref: IncreasedLatency2 }
...

This resulted in the following JSON definition:

        "AlarmConfiguration": {
          "Alarms": [
            {
              "Name": "Fn::If"
            }
          ], 
          "Enabled": true
        }, 

It looks like SAM is trying to provide shorthand syntax for supporting alarms; when SAM transforms this section, it needs to transform the alarms to be Name: <alarm-name>.

SAM does this transformation here: https://github.com/awslabs/serverless-application-model/blob/master/samtranslator/model/preferences/deployment_preference_collection.py#L104

A possible fix might be to explicitly add support for Fn::If for this property. If Fn::If is encountered here, we need to do the Name: <alarm-name> transformation on all items inside of the conditional. This would also need to be aware of other values common to Fn::If, like AWS::NoValue.

Originally posted by @keetonian in #350 (comment)

[sriram-mv]

PR has been released.