vty: Allow using hex representations in cmd numeric ranges

Ranges can now be specified in hexadecimal notation. In this case, only
hexadecimal values are accepted (prefixed with "0x").

In order to allow using a hexadecimal value as an input argument, the
command must specify the range in hexadecimal form.
This way all existing commands (decimal) won't get an hexadecimal value
unless they are further extended in the future, avoiding hard to notice
breakage due to use of stroul() without using base=0 or even worse,
using atoi() directly (which only understands decimal and provides no
error checking mechanism).

A command argument can be expanded to accept both decimal and hex in a
range by means of specifying both, example:
"mycmd (<0-255>|<0x0-0xff>)".

Related: OS#5631
Change-Id: Ia2b7fbbf5502c28374c21dbff548232680da27d4
diff --git a/tests/vty/vty_test.err b/tests/vty/vty_test.err
index 1cb4190..b021425 100644
--- a/tests/vty/vty_test.err
+++ b/tests/vty/vty_test.err
@@ -65,3 +65,13 @@
 Got VTY event: 2
 Got VTY event: 1
 Got VTY event: 3
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 1
+Got VTY event: 3