stats/vty: Add stats configuration

This commit provides stats configuration similar to the log
configuration.

The following vty commands are added to the config node:
  stats reporter statsd          Create/Modify a statsd reporter
  no stats reporter statsd       Remove a statsd reporter

To actually configure a reporter, the config-stats node is entered
when the "stats reporter" command has succeeded. The following new
vty commands are available there:
  local-ip ADDR          Set the IP address to which we bind locally
  no local-ip            Do not bind to a certain IP address
  remote-ip ADDR         Set the remote IP address to which we connect
  remote-port <1-65535>  Set the remote port to which we connect
  prefix PREFIX          Set the item/counter name prefix
  no prefix              Do not use a prefix
  enable                 Enable the reporter
  disable                Disable the reporter

Sponsored-by: On-Waves ehf
diff --git a/tests/vty/vty_test.ok b/tests/vty/vty_test.ok
index 0ea2dab..c636590 100644
--- a/tests/vty/vty_test.ok
+++ b/tests/vty/vty_test.ok
@@ -24,11 +24,11 @@
 Going to execute 'configure terminal'
 Returned: 0, Current node: 4 '%s(config)# '
 Going to execute 'line vty'
-Returned: 0, Current node: 8 '%s(config-line)# '
+Returned: 0, Current node: 9 '%s(config-line)# '
 Going to execute 'exit'
 Returned: 0, Current node: 4 '%s(config)# '
 Going to execute 'line vty'
-Returned: 0, Current node: 8 '%s(config-line)# '
+Returned: 0, Current node: 9 '%s(config-line)# '
 Going to execute 'end'
 Returned: 0, Current node: 3 '%s# '
 Going to execute 'configure terminal'
@@ -36,7 +36,7 @@
 Going to execute 'log stderr'
 Returned: 0, Current node: 7 '%s(config-log)# '
 Going to execute 'line vty'
-Returned: 0, Current node: 8 '%s(config-line)# '
+Returned: 0, Current node: 9 '%s(config-line)# '
 Going to execute 'log stderr'
 Returned: 0, Current node: 7 '%s(config-log)# '
 Going to execute 'end'