TestNewSSHClient flake: Error running "foo": wait: remote command exited

[tstromberg]

As seen at https://travis-ci.org/kubernetes/minikube/builds/536576254?utm_source=github_status&utm_medium=notification and on other builds:

ok  	k8s.io/minikube/pkg/minikube/service	0.028s	coverage: 40.7% of statements
--- FAIL: TestNewSSHClient (0.19s)
    sshutil_test.go:53: Error running command: foo
FAIL
coverage: 75.0% of statements
FAIL	k8s.io/minikube/pkg/minikube/sshutil	0.197s
ok  	k8s.io/minikube/pkg/minikube/tunnel	2.073s	coverage: 64.5% of statements
ok  	k8s.io/minikube/pkg/util	0.847s	coverage: 51.7% of statements
make: *** [test] Error 16
The command "make test" exited with 2.

Based on the timing, this may be related by recent updates to sshutil and supporting libraries that fixed lint errors.

[tstromberg]

Although we now have better logs, this is still an issue:

--- FAIL: TestNewSSHClient (0.61s)
    ssh_mock.go:173: Listening on 127.0.0.1:37039
    ssh_mock.go:83: Accepting...
    ssh_mock.go:83: Accepting...
    ssh_mock.go:132: exec request received: &{Type:exec WantReply:true Payload:[0 0 0 3 102 111 111] ch:0xc00010c0c0 mux:<nil>}
    sshutil_test.go:60: Error running "foo": wait: remote command exited without exit status or exit signal
    ssh_mock.go:189: Stopping