node tests: Use EXEMPT_FILES for line coverage.
node tests: Use EXEMPT_FILES for line coverage.

We now have 100% line coverage on 71 JS files.
This is thanks to about 150 people who have
contributed code to frontend/node_tests.

And then 126 files are still short of 100% line
coverage.

We now enforce line coverage with a set called
EXEMPT_FILES, which are the files for which
we do NOT expect to have 100% coverage.

Using an exemption list makes it so that adding
a new JS file to the project without 100% line
coverage will cause the build to fail.  This will
encourage folks to be intentional about their
lack of test coverage.

punchagan/zulip,eeshangarg/zulip,andersk/zulip,kou/zulip,shubhamdhama/zulip,kou/zulip,andersk/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,punchagan/zulip,andersk/zulip,shubhamdhama/zulip,synicalsyntax/zulip,hackerkid/zulip,eeshangarg/zulip,brainwane/zulip,rht/zulip,rht/zulip,synicalsyntax/zulip,eeshangarg/zulip,punchagan/zulip,showell/zulip,shubhamdhama/zulip,hackerkid/zulip,showell/zulip,timabbott/zulip,brainwane/zulip,shubhamdhama/zulip,showell/zulip,brainwane/zulip,showell/zulip,showell/zulip,rht/zulip,punchagan/zulip,andersk/zulip,hackerkid/zulip,timabbott/zulip,timabbott/zulip,zulip/zulip,synicalsyntax/zulip,synicalsyntax/zulip,timabbott/zulip,brainwane/zulip,hackerkid/zulip,eeshangarg/zulip,kou/zulip,shubhamdhama/zulip,rht/zulip,shubhamdhama/zulip,punchagan/zulip,timabbott/zulip,kou/zulip,kou/zulip,punchagan/zulip,punchagan/zulip,andersk/zulip,showell/zulip,synicalsyntax/zulip,timabbott/zulip,synicalsyntax/zulip,zulip/zulip,brainwane/zulip,hackerkid/zulip,andersk/zulip,synicalsyntax/zulip,timabbott/zulip,hackerkid/zulip,brainwane/zulip,shubhamdhama/zulip,zulip/zulip,zulip/zulip,kou/zulip,hackerkid/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,brainwane/zulip,kou/zulip,eeshangarg/zulip,zulip/zulip,showell/zulip,zulip/zulip,zulip/zulip