This commit adds CLI support for management VRF using l3dev. mVRF can
be enabled using config vrf add mgmt and deleted using config vrf del mgmt.
Show commands for management VRF are added which displays the linux command
output, will update show command display after concluding what would be the
output for the show commands.
Added cli to configure management interface(eth0), config interface ip eth0
add can be used to configure eth0 ip and config ip eth0 remove is used to
remove eth0 ip.

New cli config/show commands:

config vrf add mgmt
config vrf del mgmt
config interface eth0 ip add ip/mask gatewayIP
config interface eth0 ip remove ip/mask

show mgmt-vrf
show mgmt-vrf route
show mgmt-vrf addresses
show mgmt-vrf interfaces

Signed-off-by: Harish Venkatraman <harish_venkatraman@dell.com>