Add reason code to error message

[kt474]

Summary

fixes #691

Example:

IBMJobFailureError: 'Job failed: Error code 9999; Internal Error'

Details and comments

[coveralls]

Pull Request Test Coverage Report for Build 5789144076

• 0 of 4 (0.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 51.127%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit_ibm_provider/job/ibm_circuit_job.py	0	4	0.0%

Files with Coverage Reduction	New Missed Lines	%
qiskit_ibm_provider/job/ibm_circuit_job.py	1	47.92%

Totals
Change from base Build 5789141926:	-0.02%
Covered Lines:	3312
Relevant Lines:	6478

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💛 - Coveralls

[kt474]

@SooluThomas fyi

[merav-aharoni]

Looks fine.
Two tiny suggestions.
Also, I think it is worth adding a check to one of the tests where there is an error message, to check the code as well.