MXS-1889 Add test

If all slaves are down, a connection should be created to the
master.

maxscale-system-test/mxs1889.cpp

@@ -0,0 +1,36 @@
+/**
+ * MXS-1889: A single remaining master is valid for readconnroute configured with 'router_options=slave'
+ *
+ * https://jira.mariadb.org/browse/MXS-1889
+ */
+
+#include "testconnections.h"
+
+int main(int argc, char** argv)
+{
+    TestConnections test(argc, argv);
+
+    // Give some time for things to stabilize.
+    sleep(2);
+
+    // Take down all slaves.
+    test.repl->stop_node(1);
+    test.repl->stop_node(2);
+    test.repl->stop_node(3);
+
+    // Give the monitor some time to detect it
+    sleep(5);
+
+    test.maxscales->connect();
+
+    // Should succeed.
+    test.try_query(test.maxscales->conn_slave[0], "SELECT 1");
+
+    int rv = test.global_result;
+
+    test.repl->start_node(3);
+    test.repl->start_node(2);
+    test.repl->start_node(1);
+
+    return rv;
+}