Merge pull request #10 from Seagate/features/p2p-error-handling

* `NO_SPACE` indicates that the drive is full. There are background processes which may free space, so this error may occur once, and not on subsequent tries even though no data has been explicitly removed. Similarly, executing a delete may not immediately free space, so a `PUT` which fails with this error may not immediately succeed even after a `DELETE` which should free space.

* `NO_SUCH_HMAC_ALGORITHM` indicates that the `hmacAlgorithm` field in the `Security` message was invalid.

* `INVALID_REQUEST` indicates that the request is not valid. Subsequent attempts with the same request will return the same code. Examples: GET does not specify keyValue message, GETKEYRANGE operation does not specify startKey, etc.

* `NOT_ATTEMPTED` indicates that a P2P operation was received but was not even attempted due to some other error halting execution early.

* `REMOTE_CONNECTION_ERROR` indicates that a P2P operation was attempted but could not be completed.

* `NESTED_OPERATION_ERRORS` indicates that a P2P request completed but that an operation (possibly nested) failed.

* `EXPIRED` indicates that an operation did not complete in the alotted time.

A number of error codes are defined in the protocol file but not currently used:

* `NOT_ATTEMPTED`

* `HEADER_REQUIRED`

* `SERVICE_BUSY`

* `EXPIRED`

* `DATA_ERROR`

* `PERM_DATA_ERROR`

* `REMOTE_CONNECTION_ERROR`

It is possible that an error will occur that will prevent the Kinetic Device from returning a `protobuf` message with a status code. These are some situations:

  }

  body {

    p2pOperation {

      // See below for a description of error handling

      allChildOperationsSucceeded: false,

      operation {

        key: "..."

        newKey: "..."

            port: ...

            tls: false

          }

          // See below for a description of error handling

          allChildOperationsSucceeded: false,

          operation {

            key: "..."

			status {

          operation: {

          	key: "...",

          	status {

          		code: SUCCESS

          		code: NESTED_OPERATION_ERRORS

          	}

          }

        }

Error Cases:

* `code=NOT_FOUND` if the key is not found on the source peer. The push will not be attempted

* `code=INTERNAL_ERROR`

	* if there is a version mismatch between the operation's version and the destination peer's dbVersion

	* if an unexpected malfunction occurs.

If the command does not start or is terminated early, the status will be reflect that error.

If the request completed but some operations encountered errors, the message will be `NESTED_OPERATION_ERRORS`.

If all operations and nested P2P Operations within the top-level operation are successful, the `Status.code` in the `Command` message will be `SUCCESS`.

For each P2POperation, if any of it's nested operations fail, then it will have the flag `allChildOperationsSucceeded` set to false. Otherwise, that flag will be set to true.

Any operation may fail for the same reason any `PUT` could fail. Operation's have their own `Status` message to report these failures.

In addition to the failures observed by `PUT`, Operations may experience:

* `NOT_ATTEMPTED` The top level request was aborted before this operation could be attempted, either due to timeouts or another error (e.g. an IO error).

* `REMOTE_CONNECTION_ERROR` The operation was attempted, but an error prevented the operation from completing.

      // The request is not valid. Subsequent attempts with the same request will return the same code.

      // Examples: GET does not specify keyValue message, GETKEYRANGE operation does not specify startKey, etc

      INVALID_REQUEST = 16;

      // For P2P Requests, the operation was executed successfully but some nested operations

      // did not succeed. This indicates that callers should review the status of nested operations.

      // This status should only be used in the Command > Status, not in the Status messages

      // of nested P2POperations

      NESTED_OPERATION_ERRORS = 17;

    }

  }

    // List of operations to be performed.

    repeated Operation operation = 2;

    // Indicates whether all operations have Status SUCCESS

    // When false, clients should traverse Operation status codes to discover

    // error cases.

    // When true, no further error checking should be required.

    optional bool allChildOperationsSucceeded = 3;

    message Operation {

      // the key of the entry to move

      optional bytes key = 3;