[ZEPPELIN-6632] Pass the ipynb extension without a leading dot when exporting a note

[dev-donghwan]

What is this PR for?

Exporting a note to ipynb from the classic UI downloads a file with two dots before the extension, e.g. test sh..ipynb.

saveAsService.saveAs() joins the file name and the extension with a dot itself, and every other call site passes the extension without one ('zpln', 'csv', 'tsv'), as does the New UI's SaveAsService. The ipynb call site passes '.ipynb'.

ZEPPELIN-4823 meant to produce {note_name}.ipynb and replaced 'zepl.ipynb' with '.ipynb', but saveAs() already added the dot at that time, so the result became {note_name}..ipynb.

This passes 'ipynb', so the call site follows the same convention as the others.

What type of PR is it?

Bug Fix

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-6632

How should this be tested?

websocket-event.factory.test.js now replaces saveAsService with a spy and checks that a CONVERTED_NOTE_NBFORMAT message saves with 'ipynb'. The test fails with the previous '.ipynb' argument.

I also checked the resulting download name with the real saveAsService by capturing the anchor's download attribute: test sh..ipynb before the change, test sh.ipynb after.

• zeppelin-web karma suite: 194 tests pass

[tbonelee]

Merged into master