Add PostgreSQL promotion database gate

tests/test-promote-database-gate.sh

@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT="$(CDPATH= cd -- "$(dirname -- "$0")/.." && pwd)"
+FILE="$ROOT/ocf/loxthelion/managed-container.d/applications/postgresql/promote.sh"
+FAKE="$(mktemp)"
+
+cleanup()
+{
+    rm -f "$FAKE"
+}
+
+trap cleanup EXIT
+
+ocf_log()
+{
+    :
+}
+
+export OCF_RESOURCE_INSTANCE=postgresql-ha
+export MC_PROXY_CLIENT="$FAKE"
+
+# Valid disagreement.
+cat > "$FAKE" <<'EOF'
+import json
+print(json.dumps({
+    "ocf_rc": 1,
+    "ready": False,
+    "mutation": False,
+}))
+EOF
+
+chmod 0755 "$FAKE"
+
+# shellcheck disable=SC1090
+. "$FILE"
+
+unset MC_PROMOTE_DATABASE_GATE
+mc_pg_promote_database_shadow
+
+export MC_PROMOTE_DATABASE_GATE=true
+
+if mc_pg_promote_database_shadow; then
+    echo "FAIL: promotion mismatch was not gated"
+    exit 1
+fi
+
+# Transport failure.
+cat > "$FAKE" <<'EOF'
+raise SystemExit(10)
+EOF
+
+chmod 0755 "$FAKE"
+
+unset MC_PROMOTE_DATABASE_GATE
+mc_pg_promote_database_shadow
+
+export MC_PROMOTE_DATABASE_GATE=true
+
+if mc_pg_promote_database_shadow; then
+    echo "FAIL: promotion transport failure was not gated"
+    exit 1
+fi
+
+# Positive daemon agreement must still pass with the gate enabled.
+cat > "$FAKE" <<'EOF'
+import json
+print(json.dumps({
+    "ocf_rc": 0,
+    "ready": True,
+    "mutation": False,
+}))
+EOF
+
+chmod 0755 "$FAKE"
+
+export MC_PROMOTE_DATABASE_GATE=true
+
+mc_pg_promote_database_shadow
+
+echo "PROMOTE_DATABASE_GATE_RUNTIME_TEST_PASS=1"