Should check if probe is already running when launch in standalone mode on Docker for Mac

[errordeveloper]

Having launched Scope with a service token first, subsequent launch is standalone mode results in app being launched and probe failing to launch, due to split launch on Docker for Mac (see #1411 for background).

[errordeveloper]

> ./scope launch --service-token=blah
11cd9f5d4923bf7e2486a19515817205f9eb080e08639652edb2112cf6559374
> ./scope launch
23261b413ce9316ab9b04c0c327b465a40857b81d059eb400817081568736d05
weavescope is already running.