Skip tests when heat is unavailable

Currently the [service_available] heat parameter is not actually used
and the plugin tests are always executed regardless of availability
of Heat service.

This change ensures that the parameter is honored so that users can
disable plugin tests even if the plugin package is enabled.

Change-Id: I148d7a9c92f210d4584798131a1b23f648f6e5e3
diff --git a/releasenotes/notes/honor-service_available-heat-03755bb4b092e753.yaml b/releasenotes/notes/honor-service_available-heat-03755bb4b092e753.yaml
new file mode 100644
index 0000000..d0d273d
--- /dev/null
+++ b/releasenotes/notes/honor-service_available-heat-03755bb4b092e753.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    The ``[service_available] heat`` parameter now takes effect and disables
+    all tests when it is set to ``False``.