Extend tier0 coverage

Replace the existing STI smoke test with a reference to the top tie of
https://gitlab.com/redhat/centos-stream/tests/gcc-toolset-metapackage

.fmf/version

@@ -0,0 +1 @@
+1

plans/tier0.fmf

@@ -0,0 +1,29 @@
+# Tier 0 test plan. It's actually Tier 1
+#   - limited to its public part
+#   - executed on the architecture at hand
+# When run by osci.tier0 on CentOS Stream or RHEL, it receives the following
+# context:
+#   arch=x86_64 (the architecture at hand, currently OSCI uses just x86_64)
+#   distro=rhel<M>.<m> (even for CentOS Stream builds)
+#   trigger=build
+
+summary: Tier 0 test plan
+context:
+  component: gcc-toolset-15
+discover:
+  - name: collect_info
+    how: shell
+    tests:
+      - name: /info/rpms
+        test: rpm -qa --last
+  - name: public_tests
+    how: fmf
+    url: https://gitlab.com/redhat/centos-stream/tests/gcc-toolset-metapackage.git
+    filter: tier:1
+execute:
+  how: tmt
+prepare+:
+  how: shell
+environment+:
+  COLLECTIONS: gcc-toolset-15
+  WITH_SCL: "scl enable gcc-toolset-15"

tests/gts-smoketest/PURPOSE

@@ -1,3 +0,0 @@
-Test Name: gts-smoketest
-Author:
-Short Description: Check the metapackage installability

tests/gts-smoketest/runtest.sh

@@ -1,10 +0,0 @@
-#!/bin/sh
-
-set -e
-set -x
-
-# This is a metapackage.  It's main purpose is to pull other packages
-# into play via the rpm deps.
-rpm -q gcc-toolset-15
-echo
-echo RESULT: PASS

tests/tests.yml

@@ -1,10 +0,0 @@
----
-- hosts: localhost
-  roles:
-  - role: standard-test-basic
-    tags:
-    - classic
-    tests:
-    - gts-smoketest
-    required_packages:
-    - scl-utils