tests/tdef: rename the binaries to end with '_test'

It's the usual naming for unit test binaries.  Without the '_test' endig,
the tdef_vty_test_{config_root,config_subnode,dynamic} binaries do not
match the 'tests/*/*_test' pattern and appear as untracked files in git.

Change-Id: I828fa45132e11a41c527d4b25df850c19871cb75
diff --git a/src/vty/tdef_vty.c b/src/vty/tdef_vty.c
index 09459f1..bd209ae 100644
--- a/src/vty/tdef_vty.c
+++ b/src/vty/tdef_vty.c
@@ -242,7 +242,7 @@
 
 /*! Write current timer configuration arguments to the vty. Skip all entries that reflect their default value.
  * The passed prefix string must contain both necessary indent and the VTY command the specific implementation is using.
- * See tdef_vty_test_config_subnode.c and tdef_vty_test_dynamic.c for examples.
+ * See tdef_vty_config_subnode_test.c and tdef_vty_dynamic_test.c for examples.
  * \param[in] vty  VTY context.
  * \param[in] tdefs  Array of timers to print, ended with a fully zero-initialized entry.
  * \param[in] prefix_fmt  Arbitrary string to start each line with, with variable printf like arguments.