Add support for multiple runtime error messages

Storing all the runtime errors makes it possible to return all of them
them via the REST API. MaxAdmin will still only show the latest error but
MaxCtrl will now show all errors if more than one error occurs.

server/core/json_api.cc

@@ -11,7 +11,7 @@
  * Public License.
  */
 
-#include <maxscale/json_api.h>
+#include <maxscale/json_api.hh>
 
 #include <string>
 
@@ -207,6 +207,24 @@ json_t* mxs_json_error(const char* format, ...)
     return json_error(message);
 }
 
+json_t* mxs_json_error(const std::vector<std::string>& errors)
+{
+    json_t* rval = nullptr;
+
+    if (!errors.empty())
+    {
+        auto it = errors.begin();
+        rval = json_error(it->c_str());
+
+        for (it = std::next(it); it != errors.end(); ++it)
+        {
+            rval = mxs_json_error_append(rval, it->c_str());
+        }
+    }
+
+    return rval;
+}
+
 static json_t* json_error_append(json_t* obj, const char* message)
 {
     json_t* err = json_error_detail(message);