Improve timeout for dhcp response waiter
Improve timeout for dhcp response waiter

Dhcp checker tool is not always receives info
on dhcp servers in network
To make checking on network with 400 vlans it takes
7 min to perform
Also get_probing_info takes same time for this number of vlans

Change-Id: I03cac773030ccfd6c6f433e117ea9240d787bbbe
Closes-Bug: #1247284

eayunstack/fuel-astute,stackforge/fuel-astute,eayunstack/fuel-astute,stackforge/fuel-astute