Create azure clients using baseURI

[piyush-nimbalkar]

• To support azure clouds like USGovernment, China, Germany clouds, azure sdk expects the clients to pass the management base URI when creating clients.
• Creating a new config object to be passed to NewClient as it is taking lot of args already.
• Changed NewClientFromMetadata to query only compute metadata

[codecov-io]

Codecov Report

Merging #57 into master will decrease coverage by 0.00%. The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master     #57      +/-   ##
=========================================
- Coverage    7.52%   7.51%   -0.01%     
=========================================
  Files          14      14              
  Lines        3058    3061       +3     
=========================================
  Hits          230     230              
- Misses       2820    2823       +3     
  Partials        8       8              

Impacted Files	Coverage Δ
azure/azure.go	0.57% <0.00%> (-0.02%)	:arrow_down:
azure/base_vmsclient.go	0.00% <0.00%> (ø)
azure/scaleset_vmsclient.go	0.00% <0.00%> (ø)
azure/vmsclient.go	0.00% <0.00%> (ø)

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