When the azure service is unavailable, the error message returned does not contain the error node

[zjy282]

Describe the change
The Json deserialization function of the custom structure ErrorResponse returns the correct and expected message copy for the case where there is no error node in the APIError return information.

Describe your solution
In the custom ErrorResponse structure json deserialization function, judge whether the error node is included, if not, get the message node as the error message, if not, use the response body as the error message.

Tests
Please refer to the TestErrorResponse function in error_test.go.

Issue: When the azure service is unavailable, the error message returned does not contain the error node
For example:

{
    "statusCode": 500,
    "message": "Internal server error",
    "activityId": ""
}

[codecov]

Codecov Report

Merging #464 (4c75ca8) into master (71a2493) will decrease coverage by 0.35%.
The diff coverage is 82.35%.

@@            Coverage Diff             @@
##           master     #464      +/-   ##
==========================================
- Coverage   97.05%   96.71%   -0.35%     
==========================================
  Files          17       17              
  Lines         714      731      +17     
==========================================
+ Hits          693      707      +14     
- Misses         15       17       +2     
- Partials        6        7       +1     

Files Changed	Coverage Δ
error.go	95.16% <82.35%> (-4.84%)	⬇️