Add monitor TLS test case

Added a test that verifies the server state is Down when the backend
doesn't support TLS.

maxscale-system-test/mxs2878_monitor_ssl.cpp

@@ -0,0 +1,35 @@
+/**
+ * Covers the following bugs:
+ * MXS-2878: Monitor connections do not insist on SSL being used
+ * MXS-2896: Server wrongly in Running state after failure to connect
+ */
+
+#include "testconnections.h"
+#include <sstream>
+
+std::string join(StringSet st)
+{
+    std::ostringstream ss;
+
+    for (const auto& a : st)
+    {
+        ss << a << " ";
+    }
+
+    return ss.str();
+}
+
+int main(int argc, char** argv)
+{
+    TestConnections test(argc, argv);
+
+    for (auto srv : {"server1", "server2", "server3", "server4"})
+    {
+        StringSet expected = {"Down"};
+        auto status = test.maxscales->get_server_status(srv);
+        test.expect(status == expected,
+                    "Expected '%s' but got '%s'", join(expected).c_str(), join(status).c_str());
+    }
+
+    return test.global_result;
+}