Unwrap DecoderExceptions on connections (OriginConnectExceptions) into RequestAttempts

[gavinbunney]

During origin connection failures, netty throws a DecoderException. Currently it is passed through to RequestAttempt and falls into the basic OriginConnectException handling, that is, only the base class name is emitted.

This change unwraps the DecoderException before creating the OriginConnectException so the underlying cause is better propagated. This change also then further unwraps theOriginConnectException in the RequestAttempt class during ssl handshake failures so we know the actual cause of the ssl handshake failure.

Before:

{
  "error": "ORIGIN_CONNECT_ERROR",
  "exceptionType": "DecoderException",
  "status": -1,
  "duration": 42266,
  "attempt": 1,
  "region": "us-east-1",
  "availabilityZone": "us-east-1c",
  "asg": "myapp-v103",
  "instanceId": "i-123abc",
  "vip": "myapp-",
  "ipAddress": "10.0.0.1",
  "port": 443,
  "readTimeout": 600000,
  "connectTimeout": 1500
}

After:

{
  "error": "ORIGIN_CONNECT_ERROR",
  "cause": "Certificate application name (myapp) does not match expected name: mysecondapp",
  "exceptionType": "SSLHandshakeException",
  "status": -1,
  "duration": 42266,
  "attempt": 1,
  "region": "us-east-1",
  "availabilityZone": "us-east-1c",
  "asg": "myapp-v103",
  "instanceId": "i-123abc",
  "vip": "myapp-",
  "ipAddress": "10.0.0.1",
  "port": 443,
  "readTimeout": 600000,
  "connectTimeout": 1500
}

[jguerra]

LGTM