Merge pull request #73 from Ouranosinc/nbval-default-ignore-html-and-…

…javascript-output

Nbval default ignore html and javascript output

# Overview

Ignore by default html and javascript output to decrease usage of `NBVAL_IGNORE_OUTPUT`.

## Changes

- Adds `conftest.py` following https://nbval.readthedocs.io/en/latest/index.html?highlight=skip#Skipping-certain-output-types

## Related Issue / Discussion

- Probably will avoid us needing `--nbval-lax`.
- Tested with Raven notebooks http://jenkins.ouranos.ca/job/PAVICS-e2e-workflow-tests/job/nbval-default-ignore-html-and-javascript-output/2/console all diff from xarray html output are gone

## Additional Information

Nbval documentation was not 100% correct: computationalmodelling/nbval#168

conftest.py

@@ -0,0 +1,3 @@
+def pytest_collectstart(collector):
+    if collector.fspath and collector.fspath.ext == '.ipynb':
+        collector.skip_compare += 'text/html', 'application/javascript',