Bug 7900: make feature repos aggregate features

Bug 7900: make feature repos aggregate features

Instead of redefining features and producing standalone feature
repositories, feature-repo-parent can produce features which list the
individual feature repositories produced by single-feature-parent.
This allows integration/distribution's integration-index to build much
faster (by rendering SFT moot there).

SFT now tests individual features in single-feature-test instead of
testing the full repository. This makes the -Psft profile useless so
it is removed. It also means that odl-bundles-test needs to be handled
specially, since it is used in features4-test: it can't use
single-feature-parent, otherwise it introduces a dependency loop. This
patch introduces a new, internal parent,
untested-single-feature-parent, which is used by odl-bundles-test and
single-feature-parent: untested- takes care of the actual feature
construction, and single-feature-parent adds the SFT tests.

Change-Id: Ib0de6ce1e6488944bcbe0aa7e84496676f6db19a
Signed-off-by: Stephen Kitt <skitt@redhat.com>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>