Fix #294 - Reliable indication of Azure

[nfx]

• DatabricksClient.IsAzure is checking for both resource id and workspace hostname
• Added more unit test coverage for ClustersAPI
• Fixed version linking

[TravisBuddy]

Hey @nfx,
Your changes look good to me!

View build log

TravisBuddy Request Identifier: 3715ae80-f381-11ea-addc-35ae975c2fab

[codecov-commenter]

Codecov Report

Merging #312 into master will increase coverage by 0.71%.
The diff coverage is 38.88%.

@@            Coverage Diff             @@
##           master     #312      +/-   ##
==========================================
+ Coverage   64.18%   64.90%   +0.71%     
==========================================
  Files          55       55              
  Lines        6741     6744       +3     
==========================================
+ Hits         4327     4377      +50     
+ Misses       2044     1996      -48     
- Partials      370      371       +1     

Impacted Files	Coverage Δ
common/client.go	73.22% <0.00%> (ø)
compute/model.go	95.65% <ø> (ø)
internal/qa/testing.go	48.93% <20.00%> (-0.71%)	⬇️
compute/clusters.go	81.50% <66.66%> (+20.60%)	⬆️
compute/common_instances.go	73.33% <100.00%> (ø)
provider/provider.go	91.85% <100.00%> (+2.55%)	⬆️

[sdebruyn]

This will cover 99% of the cases, however, users can use custom hostnames. Maybe an optional string in the provider to explicitly set it to AWS or Azure can help us? Or an API endpoint just letting us know which cloud we're working with.