fix: [Workaround] CNTKModel does not output correct result

[memoryz]

Workaround for #1075 : CNTKModel does not output correct result for ResNet50 model when running on Databricks.
@mhamilton723 discovered adding a cache call works around the issue.

[welcome]

💖 Thanks for opening your first pull request! 💖 We use semantic commit messages to streamline the release process. Before your pull request can be merged, you should make sure your first commit and PR title start with a semantic prefix. This helps us to create release messages and credit you for your hard work!
Examples of commit messages with semantic prefixes:

• fix: Fix LightGBM crashes with empty partitions
• feat: Make HTTP on Spark back-offs configurable
• docs: Update Spark Serving usage
• build: Add codecov support
• perf: improve LightGBM memory usage
• refactor: make python code generation rely on classes
• style: Remove nulls from CNTKModel
• test: Add test coverage for CNTKModel

Make sure to check out the developer guide for guidance on testing your change.

[memoryz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

Merging #1076 (9f5b024) into master (36ee274) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1076      +/-   ##
==========================================
- Coverage   84.95%   84.90%   -0.05%     
==========================================
  Files         206      206              
  Lines        9751     9752       +1     
  Branches      550      564      +14     
==========================================
- Hits         8284     8280       -4     
- Misses       1467     1472       +5     

Impacted Files	Coverage Δ
.../scala/com/microsoft/ml/spark/cntk/CNTKModel.scala	83.33% <100.00%> (+0.07%)	⬆️
...ala/org/apache/spark/ml/param/DataFrameParam.scala	69.56% <0.00%> (-17.40%)	⬇️
...a/com/microsoft/ml/spark/io/http/HTTPClients.scala	73.33% <0.00%> (-3.34%)	⬇️
...rosoft/ml/spark/stages/PartitionConsolidator.scala	95.74% <0.00%> (+2.12%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 36ee274...9f5b024. Read the comment docs.

[memoryz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[memoryz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[welcome]

Congrats on merging your first pull request, we appreciate your support! 🎉🎉🎉