Promote openStandardStreams sub-tests to top level

Promote openStandardStreams sub-tests to top level

Commit a72468e820c2922540737c053eef27d033c2e77b split the test into two
functions, but kept them combined in a single slot for QTest to invoke.

That being the case, we might as well have them as test functions of
their own right. Should work nicer with test failures, skips and such.

Change-Id: I62c1fc7777c08b3e87a5903632d73dc1e1d97e1a
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>