BGP: Implement key show commands for all VRFs

BGP: Implement key show commands for all VRFs

Key BGP 'show' commands have been expanded to support 'vrf all':

show ip bgp vrf all summary
show ip bgp vrf all neighbors
show ip bgp vrf all nexthop
show ip bgp vrf all update-group
show ip bgp vrf all
show bgp vrf all summary
show bgp vrf all update-group
show bgp vrf all

Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by:   Don Slice <dslice@cumulusnetworks.com>
Ticket: CM-10402
Reviewed By: CCR-4466
Testing Done: Manual