Show and clear command support

The following show and clear commands support Multicast Multi-VRF:

clear ip igmp [ vrf vrf-name ] cache
clear ip igmp [ vrf vrf-name ] traffic
show ip igmp [vrf vrf-name] group [group-address [detail] [tracking]]
show ip igmp [vrf vrf-name] interface [ve number | ethernet unit/slot/port | tunnel num]
show ip igmp [vrf vrf-name] settings
show ip igmp [vrf vrf-name] traffic