Increase tolerance of install DHCP

For Ubuntu, added the following kernel options:
netcfg/link_detection_timeout=20
netcfg/dhcptimeout=120
For CentOS:
dhcptimeout=120

Closes-Bug: #1381266
Related-Bug: #1376680
Related-Bug: #1379917
blueprint 100-nodes-support

Change-Id: I8bf38ae18b5741b03e6bda5f8e69748a8ecdf2ec