Web: allow to run extension tests

[bpasero]

Currently seems to not set the extension tests path properly.

[weinand]

There are two issues:

• the environment attribute 'extensionTestsPath' needs to be passed properly.
• when running VS Code in the web UI or in a remote setup, the value of the extensionTestsPath attribute must be a valid path that exists in the filesystem. This is a problem because for historical reasons the path generated by yeoman is ${workspaceFolder}/out/test/suite/index which does not exist in the filesystem (because it lacks the file extension .js). When running tests locally, the non-existing path is not an issue because mocha will find the tests anyway.

The first problem has been fixed in VS Code.

The second problem requires a change in "node-debug2": we have to cope with paths that lack a ".js" extension. I've created microsoft/vscode-node-debug2#245 to address this.

Without the second fix a workaround is needed in order to run extension tests in the Web or remote scenarios successfully: just append the ".js" extension to the ${workspaceFolder}/out/test/suite/index path.

[bpasero]

Verification: open a hello world extension in the web and run its unit tests.

[weinand]

One issue left: the tab where the VS Code instance runs the tests is not closed automatically at the end. See bug #83281.

[roblourens]

I hadn't published node2 with the fix. Doing that now, we can reverify this tomorrow.

[weinand]

Verification is trivial:

• open a hello world extension in the web and run its unit tests.

[alexr00]

Verified using https://github.com/microsoft/vscode-extension-samples/tree/master/helloworld-test-sample and running the tests.