Add RHEL gating test

gating.yaml

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+--- !Policy
+product_versions:
+  - rhel-*
+decision_context: osci_compose_gate
+rules:
+  - !PassingTestCaseRule {test_case_name: osci.brew-build.tier0.functional}

tests/basic-test.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -
+set -e
+set -x
+
+# Just check that dune works.
+dune --version

tests/tests.yml

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+- hosts: localhost
+  roles:
+  - role: standard-test-basic
+    tags:
+    - classic
+    required_packages:
+    - ocaml
+    - ocaml-dune
+    tests:
+    - simple:
+        dir: .
+        run: ./basic-test.sh