Add retry information to ResponseMetadata

[jamesls]

This pulls in #965 with the following changes:

• Replace Retries list with the number of retry attempts.
• Update ClientError messages to include retry information when max attempts are reached.

More context here.

A few examples:

Client error messages:

An error occurred (NotFound) when calling the DescribeInstances operation (max_retries=4 reached): The instance ID 'i-1234' does not exist

ResponseMetadata on error:

 'ResponseMetadata': {'HTTPHeaders': {'connection': 'close',
                                      'date': 'Wed, 31 Aug 2016 17:41:51 GMT',
                                      'server': 'AmazonEC2',
                                      'transfer-encoding': 'chunked'},
                      'HTTPStatusCode': 400,
                      'MaxAttemptsReached': True,
                      'RequestId': 'abcd',
                      'RetryAttempts': 4}}

ResponseMetadata on success:

 'ResponseMetadata': {'HTTPHeaders': {'content-type': 'text/xml;charset=UTF-8',
                                      'date': 'Wed, 31 Aug 2016 17:42:19 GMT',
                                      'server': 'AmazonEC2',
                                      'transfer-encoding': 'chunked',
                                      'vary': 'Accept-Encoding'},
                      'HTTPStatusCode': 200,
                      'RequestId': '25587b14-963b-4357-bc13-56c0acd52d0e',
                      'RetryAttempts': 0}}

cc @kyleknap @JordonPhillips

[codecov-io]

Current coverage is 97.57% (diff: 100%)

Merging #1024 into develop will increase coverage by <.01%

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  Methods           0          0          
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+ Hits           6700       6717    +17   
  Misses          167        167          
  Partials          0          0          

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[kyleknap]

Sort of unfortunate that retry_info has to remember to put spaces, but I do not think there is any way around it if we want to put it right between operation and the colon.

[jamesls]

Yeah. The first version I had rendered the msg, but before calling super() would mess with the msg to inject retry info. This approach seemed less worse that the first approach.

Also open to other ways to improve this.

[kyleknap]

Makes sense. I am fine with how it is now. I cannot think of any other ways.

[kyleknap]

Looks good. Just had small questions and comments.

[jamesls]

@kyleknap updated.

[kyleknap]

Thanks! 🚢 assuming the tests pass.