Use DefaultAzureCredential instead of the deprecated ServicePrincipalCredentials

[tomchop]

Closes #258

[codecov-commenter]

Codecov Report

Merging #259 into master will increase coverage by 2.62%. The diff coverage is 70.71%.

@@            Coverage Diff             @@
##           master     #259      +/-   ##
==========================================
+ Coverage   65.39%   68.01%   +2.62%     
==========================================
  Files          14       29      +15     
  Lines         968     1998    +1030     
==========================================
+ Hits          633     1359     +726     
- Misses        335      639     +304     

Flag	Coverage Δ
#nosetests	68.01% <70.71%> (+2.62%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...cloudforensics/providers/azure/internal/network.py	24.52% <24.52%> (ø)
libcloudforensics/providers/aws/internal/kms.py	40.00% <40.00%> (ø)
libcloudforensics/providers/gcp/forensics.py	54.54% <48.00%> (-10.46%)	:arrow_down:
libcloudforensics/providers/aws/forensics.py	56.16% <53.06%> (-13.61%)	:arrow_down:
...ibcloudforensics/providers/gcp/internal/compute.py	56.08% <54.28%> (-6.27%)	:arrow_down:
...cs/providers/gcp/internal/compute_base_resource.py	37.33% <54.28%> (+0.82%)	:arrow_up:
libcloudforensics/providers/aws/internal/log.py	73.07% <55.55%> (-4.20%)	:arrow_down:
...bcloudforensics/providers/gcp/internal/function.py	40.54% <62.50%> (+8.28%)	:arrow_up:
...loudforensics/providers/azure/internal/resource.py	65.38% <65.38%> (ø)
...ibcloudforensics/providers/gcp/internal/project.py	61.90% <66.66%> (-3.81%)	:arrow_down:
... and 35 more

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[hacktobeer]

Fix the mypy error and LGTM.

[tomchop]

I'll move it to drafts as Azure's libs still need more updating 👎