Variable substitution doesn't seem to work when running in extension dev host

[aeschli]

Testing #8196 on Linux

• clone https://github.com/Microsoft/vscode-node-debug.git
• npm install
• gulp compile
• run the extension with F5
• In the extension dev host try to attach to a node process

Error: Attach to process: '${command.PickProcess}' doesn't look like a process id.

It looks like variables are not detected and replaced

[weinand]

@aeschli I'm not able to reproduce this problem on elementary:

Variable substitution works fine for me.