Make it possible to flush output via newline in between tests

[onsi]

Some CI systems only flush output when a newline is observed. This makes it hard to see Ginkgo's progress when running without -v. A new mode that forces Ginkgo to emit a newline between each spec report (even if that report is just "o") would resolve this.

/cc @pohly

[pohly]

This is the gist of it. Note that we haven't actually verified that a newline will help, but it seems likely.

While you are at it, a mode where not even the o or S gets printed might also be useful. When I run -focus=one-particular-test, the screen fills up with S characters simply because we have so many tests in the Kubernetes E2E suite.

[pohly]

Or make it so that just the S gets skipped (pun intended). The o is useful when running a few tests.