vtysh: mark exit-vrf with end when using vtysh -m

vtysh: mark exit-vrf with end when using vtysh -m

VRF context blocks have a context-specific exit command in order to
explicitly force an exit to the top level config node. This command
exists because 'ip route' commands are accepted in both VRF_NODE and
CONFIG_NODE, so static routes intended to be accepted in CONFIG_NODE
that immediately follow a VRF_NODE block will be shoved into the
VRF_NODE block unless the VRF context is explicitly exited.

However, because this is a command that exits to CONFIG_NODE, vtysh -m
should be printing an `end` at the end of the context, since
frr-reload.py relies on this context ender to know when it's back in
CONFIG_NODE. But since this is the only explicit context exit command
that also exits to CONFIG_NODE we don't really have a good way of doing
this already. Hence this god-awful patch.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>