Utility function for accuracy and l2 norm [JATIC-I2-IBM]

[kieranfraser]

Description

Adding an attack-agnostic metric function to return clean and robust accuracy as well as calculation of average perturbation added to images which successfully fool classification estimator.

Fixes #2301

Type of change

Please check all relevant options.

• Improvement (non-breaking)
• Bug fix (non-breaking)
• New feature (non-breaking)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Testing

Please describe the tests that you ran to verify your changes. Consider listing any relevant details of your test configuration.

• Test A
• Test B

Test Configuration:

• OS
• Python version
• ART version or commit number
• TensorFlow / Keras / PyTorch / MXNet version

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• My changes have been tested using both CPU and GPU devices

[codecov-commenter]

Codecov Report

Merging #2302 (2b77357) into dev_1.17.0 (337a15f) will decrease coverage by 1.29%.
The diff coverage is 13.33%.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

@@              Coverage Diff               @@
##           dev_1.17.0    #2302      +/-   ##
==============================================
- Coverage       85.62%   84.34%   -1.29%     
==============================================
  Files             324      324              
  Lines           29323    29337      +14     
  Branches         5405     5406       +1     
==============================================
- Hits            25108    24744     -364     
- Misses           2837     3208     +371     
- Partials         1378     1385       +7     

Files	Coverage Δ
art/metrics/metrics.py	82.82% <13.33%> (-7.12%)	⬇️

... and 17 files with indirect coverage changes