[media] Fix "sync_keys" and "regenerate_key"

[lmazuel]

• Regenerate_key does not return MediaService:
  https://msdn.microsoft.com/en-us/library/azure/mt750386.aspx
• Add "required" to keytype in "sync_keys":
  https://msdn.microsoft.com/en-us/library/azure/mt750388.aspx

@amarzavery @BrianBlum for review

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This change is

[BrianBlum]

Need to also trim the comma after "OK"

[lmazuel]

@johanste There is no breaking change here:

• "regenerate_keys" does not return anything, Python would have returned an invalid object at best, CloudError at worst
• "keyType" is required, trying to call without it raise a CloudError

[johanste]

@lmazuel, switching a property from not required to required may be a breaking changes in some languages. We are just spinning up the breaking change review/notification process, and as of now, we are applying the tag if we think that something could be breaking in an SDK. Meaning we do expect false positives at the moment.

However, we very much appreciate your confirmation that this will not be breaking for the Python SDK :)

[lmazuel]

Adding "id" as required for "sync"
https://msdn.microsoft.com/en-us/library/azure/mt750386.aspx

[lmazuel]

@amarzavery @johanste @BrianBlum FYI:

• To be precise about impact on the Python SDK, adding "required" changes a CloudError (refused by the RestAPI after the calls) to a "TypeError: missing parameters" (with no RestAPI calls). I don't call this "breaking change", since this doesn't change working code. (I understand this statement is for Python only)
• I tested all operations and made a Python PR: azure-mgmt-media azure-sdk-for-python#855

[amarzavery]

@BrianBlum - I think the changes made in this PR are also made in #698. Hence, I think it will be safe to close this PR and let the other one get merged with all the changes.