Fix test for Go 1.12.x

Fix test for Go 1.12.x

After switching to Go 1.12, the format-string causes an error;

```
=== Errors
cli/config/config_test.go:154:3: Fatalf format %q has arg config of wrong type *github.com/docker/cli/cli/config/configfile.ConfigFile
cli/config/config_test.go:217:3: Fatalf format %q has arg config of wrong type *github.com/docker/cli/cli/config/configfile.ConfigFile
cli/config/config_test.go:253:3: Fatalf format %q has arg config of wrong type *github.com/docker/cli/cli/config/configfile.ConfigFile
cli/config/config_test.go:288:3: Fatalf format %q has arg config of wrong type *github.com/docker/cli/cli/config/configfile.ConfigFile
cli/config/config_test.go:435:3: Fatalf format %q has arg config of wrong type *github.com/docker/cli/cli/config/configfile.ConfigFile
cli/config/config_test.go:448:3: Fatalf format %q has arg config of wrong type *github.com/docker/cli/cli/config/configfile.ConfigFile

DONE 1115 tests, 2 skipped, 6 errors in 215.984s
make: *** [Makefile:22: test-coverage] Error 2
Exited with code 2
```

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit d4877fb2259feac2c76762ccd3001999cb7f0d58)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Gbp-Pq: Name test--cli-fix-golang12.patch