Regression: Don't print progress in a non-TTY context

[mgol]

Bug Report or Feature Request (mark with an x)

- [x] bug report -> please search issues before submitting
- [ ] feature request

Area

- [x] devkit
- [ ] schematics

Versions

$ node --version
v8.11.2
$ yarn --version
1.7.0

macOS High Sierra 10.13.5 (17F77)

Repro steps

See #8148.

The log given by the failure

See #8148.

Desired functionality

See #8148.

Mention any other details that might be useful

This is a regression as it worked fine in CLI 1.7.4 and no longer does in 6.0.8.