Test: language server protocol trace option

[dbaeumer]

From microsoft/vscode-languageserver-node#39

• Windows | OS X | Linux - @aeschli

Steps:

• install eslint or tslint
  • enable tracing via the setting:

    "eslint.trace.server":"messages"

or

    "tslint.trace.server":"messages"

• open output window and switch to the tslint / eslint channel
• open a ts / js file and ensure that the communication between client and server is logged.
• change the setting to: "verbose"
• ensure that you get a verbose log
• change the setting to "off"
• ensure that tracing stops.