Adapt complex selection fixtures to new changes

We don't generate anymore images if packages are empty - those are now
virtuals which just generates empty artifacts.

Virtuals are not meant to be required by other packages in build time,
because it would violate the virtual packages purpose (they are just
useful for runtime).

This test was used to verify version selection of the best match during build
time, not to actually test any build process. Inject steps so images are
actually generated, and they can depend on each others.

tests/fixtures/complex/selection/0.20191212/build.yaml

@@ -15,3 +15,6 @@ requires:
 - category: "layer"
   name: "build-sabayon-overlay"
   version: "0.20191212"
+
+steps:
+- echo "foo"

tests/fixtures/complex/selection/kernel/build.yaml

@@ -5,3 +5,6 @@ requires:
 
 includes:
 - /usr/portage/packages/.*
+
+steps:
+- echo "foo"

tests/fixtures/complex/selection/meta/build.yaml

@@ -16,3 +16,6 @@ requires:
 - category: "layer"
   name: "build-sabayon-overlay"
   version: ">=0.1"
+
+steps:
+- echo "foo"

tests/fixtures/complex/selection/sabayon-build-overlays/portage/0.20191126/build.yaml

@@ -2,3 +2,5 @@ requires:
 - category: "layer"
   name: "build"
   version: ">=0.1"
+steps:
+- echo "foo"

tests/fixtures/complex/selection/sabayon-build-overlays/portage/0.20191212/build.yaml

@@ -2,3 +2,5 @@ requires:
 - category: "layer"
   version:  "0.1"
   name:     "build"
+steps:
+- echo "foo"

tests/fixtures/complex/selection/sabayon-build-overlays/sabayon-overlay/0.20191205/build.yaml

@@ -5,3 +5,5 @@ requires:
 - category: "layer"
   name: "sabayon-build-portage"
   version: ">=0.1"
+steps:
+- echo "foo"

tests/fixtures/complex/selection/sources5.4.2/build.yaml

@@ -2,6 +2,7 @@ requires:
 - category: "layer"
   version:  "0.1"
   name:     "build-sabayon-overlays"
-
+steps:
+- echo "foo"
 includes:
 - /usr/portage/packages/.*