Multi-context - add/update/delete - ip6 vrf instances - add 10, del 5, add new 10, del 15

HLD:
config1
configure 15 pg-ip6 interfaces
add 4 vrfs (3 pg-ip6 interfaces per vrf)
test1
send ip6 packets between all pg-ip6 interfaces
verify1
check vrf data by parsing output of API ip_fib_dump
all packets received correctly in case of pg-ip6 interfaces in vrf
no packet received in case of pg-ip6 interfaces not in vrf

config2
delete 2 vrfs
test2
send ip6 packets between all pg-ip6 interfaces
verify2
check vrf data by parsing output of API ip_fib_dump
all packets received correctly in case of pg-ip6 interfaces in vrf
no packet received in case of pg-ip6 interfaces not in vrf

config3
add 1 of deleted vrfs and 1 new vrf
test3
send ip6 packets between all pg-ip6 interfaces
verify3
check vrf data by parsing output of API ip_fib_dump
all packets received correctly in case of pg-ip6 interfaces in vrf
no packet received in case of pg-ip6 interfaces not in vrf

config4
delete 4 vrfs (i.e. no vrf created)
test4
send ip6 packets between all pg-ip6 interfaces
verify4
check vrf data by parsing output of API ip_fib_dump
no packet received on all of pg-ip6 interfaces