Allow 'configure <cr>' at VTY to enter config mode

Similar to HP/Aruba, only the word or abbreviation of 'configure' is
required to enter config mode. This is the default. It is still possible
to add other configuration sources than 'terminal' if implemented in
the future.

Change-Id: I56d5d1bd5526603a397c62542e667c413f4952ca
diff --git a/src/vty/command.c b/src/vty/command.c
index e67fd86..a3e0e36 100644
--- a/src/vty/command.c
+++ b/src/vty/command.c
@@ -2997,7 +2997,7 @@
 /* Configration from terminal */
 DEFUN(config_terminal,
       config_terminal_cmd,
-      "configure terminal",
+      "configure [terminal]",
       "Configuration from vty interface\n" "Configuration terminal\n")
 {
 	if (vty_config_lock(vty))