Improve error messaging when no docker-machine VM exists

[rnorth]

e.g. in the case where the docker-machine tool is found but there's no VM.

At present the logged error is quite unhelpful:

o.t.d.DockerClientProviderStrategy       :     DockerMachineClientProviderStrategy: failed with exception InvalidConfigurationException (Exception when executing docker-machine status default)

[rnorth]

Mainly for the benefit of people using a fresh Docker Machine setup, I think we should indicate that a VM may need to be created first.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you believe this is a mistake, please reply to this comment to keep it open. If there isn't one already, a PR to fix or at least reproduce the problem in a test case will always help us get back on track to tackle this.

[vcvitaly]

I can take it.