Separate validFilename into a separate function

This will generalize it and make it callable from other places

Tested: Added test cases, they pass

Signed-off-by: Josh Lehan <krellan@google.com>
Change-Id: I8df30d6fe6753a2454d7051cc2d8813ddbf14bad
diff --git a/meson.build b/meson.build
index e8897b3..0ab48ff 100644
--- a/meson.build
+++ b/meson.build
@@ -383,6 +383,7 @@
   'include/ut/http_utility_test.cpp',
   'include/ut/human_sort_test.cpp',
   'include/ut/multipart_test.cpp',
+  'include/ut/openbmc_dbus_rest_test.cpp',
   'redfish-core/include/utils/query_param_test.cpp',
   'redfish-core/lib/ut/service_root_test.cpp',
   'redfish-core/ut/configfile_test.cpp',