fix configeth does not reload new ifcfg-* for installnic when diskless/statelite node reboot

[bybai]

The PR is to fix issue

#6028

The modification include

configeth will reload new ifcfg-* for installnic when diskless/statelite node reboot

The UT result

1. Reboot diskless node, and check xcat.log, confignetwork runs.

Fri Feb 22 04:16:23 EST 2019 [info]: xcat.deployment.postbootscript: postbootscript start..: confignetwork
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
[I]: configure the install nic eth0.
[I]: configeth on byrh07: os type: redhat
['/etc/sysconfig/network-scripts/ifcfg-eth0']
[I]: >> DEVICE=eth0
[I]: >> IPADDR=10.4.41.7
[I]: >> NETMASK=255.0.0.0
[I]: >> BOOTPROTO=none
[I]: >> ONBOOT=yes
[I]: >> HWADDR=42:66:0a:04:29:07
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

2. check install nic is not dynamic configured

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 42:66:0a:04:29:07 brd ff:ff:ff:ff:ff:ff
    inet 10.4.41.7/8 brd 10.255.255.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::4066:aff:fe04:2907/64 scope link
       valid_lft forever preferred_lft forever

[robin2008]

looks good.