[SCB-2739] fix flaky tests in clients

[anantdahiya8]

Summary

The function writeValueAsString returns the order of elements in no fix order and can hamper the functionality of mock function.
For the test #TestSendHeartBeats , these are 2 values I received from the function writeValueAsString

We are only changing the code to take any string value for the 3rd parameter and the first 2 parameter will be checked.
Similar code is present in other test functions - TestGetServiceInstanceMessage, TestDeleteServiceInstance , where all the parameters are mocked for any value.

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[codecov-commenter]

Codecov Report

Merging #3497 (0eebf52) into master (8a7f6b2) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #3497      +/-   ##
============================================
- Coverage     74.38%   74.38%   -0.01%     
  Complexity      670      670              
============================================
  Files          1589     1589              
  Lines         39830    39830              
  Branches       3633     3633              
============================================
- Hits          29628    29626       -2     
- Misses         8721     8722       +1     
- Partials       1481     1482       +1     

Impacted Files	Coverage Δ
...mb/metrics/core/meter/os/cpu/AbstractCpuUsage.java	88.88% <0.00%> (-11.12%)	⬇️
...he/servicecomb/foundation/common/net/NetUtils.java	64.80% <0.00%> (-1.61%)	⬇️
...egistry/client/http/ServiceRegistryClientImpl.java	68.45% <0.00%> (+0.38%)	⬆️

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