Pass multiple arguments to the test DebugClient to enable code coverage

[DonJayamanne]

Currently we're able to get code coverage for all tests running in an extension.
However when testing the debug adapter, we're not able to get any coverage as the the adapter launches a seprate process (child_process.spawn).

The solution to get coverate would be to change the values passed into spawn as follows:

• runtime = npx or istanbul
• executable (turned into an array) = ['cover', '<adapter.js>', '--dir', './coverage'] (basically we're passing an array instead of a string for executable

We now have code coverage.

So, the way I see it, the only change would be to turn the argument executable into a string|string[].

Possibly having to either rename the argument or creating an overloaded constructor.

[DonJayamanne]

I'm assuming the new proposed api DebugConfigurationProvider.debugAdapterExecutable in VS Code will make this possible.

[DonJayamanne]

Closing as this doesn't work, as output from istanbul in stdout/stderr will interfere with debugger.
Will need to use the other connection mechanism (using the socket)