support init behavior

[ak1ra24]

#13

[ak1ra24]

$ ./tinet init                                                                                                                                                                             

precmd:
- cmds:
  - cmd: ""
preinit:
- cmds:
  - cmd: ""
postinit:
- cmds:
  - cmd: echo hoge
postfini:
- cmds:
  - cmd: ""
nodes:
- name: R1
  type: ""
  net_base: ""
  image: slankdev/ubuntu18.04
  interfaces:
  - name: net0
    type: direct
    args: C1#net0
    addr: ""
  - name: net1
    type: bridge
    args: B0
    addr: ""
  - name: net2
    type: veth
    args: peer0
    addr: ""
  - name: net3
    type: phys
    args: ""
    addr: ""
  sysctls: []
  mounts: []
switches:
- name: B0
  interfaces:
  - name: net0
    type: docker
    args: R1
    addr: ""
  - name: net0
    type: netns
    args: R2
    addr: ""
node_configs:
- name: C0
  cmds:
  - cmd: ip link set dev net0 up
- name: C1
  cmds:
  - cmd: echo slankdev slankdev
  - cmd: |-
      echo slankdev &&
      echo slankdev
test:
- name: p2p
  cmds:
  - cmd: docker exec C0 ping -c2 10.0.0.2
  - cmd: echo hoge
- name: lo
  cmds:
  - cmd: docker exec C0 ping -c2 10.255.0.1
  - cmd: echo hoge