Introduce cmd/showalloc to show IP allocation map of dnet/cnet/tnet

[TothFerenc]

This PR introduces the showalloc command to show IP allocation map of DanmNets, ClusterNetworks and TenantNetworks.

Parameters:

• kubeconfig: to specify K8s apiserver credential
• dnet, cnet, tnet: to specify DANM network
• n: to specify namespace, by default it is default
• 6: to switch to IPv6 mode, by default the IPv4 mode is active
• showCIDR: to show the specified sub-CIDR only
• a: to show "free" and "out of pool range" IPs as well, by default these are suppressed

Example run:

# showalloc --kubeconfig .kube/config -dnet sriov-a -n kube-system
DANM network Kind: DanmNet
       IP version: IPv4
             CIDR: 10.100.100.0/24
       Pool start: 10.100.100.1
       Pool   end: 10.100.100.254
--------------------------------------------------------------
   10.100.100.0 : reserved (network base address)
   10.100.100.1 : allocated (Pod: danmtest-869444956b-vxshh)
   10.100.100.2 : allocated (Pod: danmtest-869444956b-gk2wh)
   10.100.100.3 : allocated (Pod: danmtest-869444956b-rrfpr)
   10.100.100.4 : allocated (Pod: danmtest-869444956b-z92pl)
   10.100.100.5 : allocated (Pod: danmtest-869444956b-2j2vp)
 10.100.100.255 : reserved (broadcast address)