raising proper exception for invalid allocation-pool and modifying display message for out of cidr gateway ip. This will fix 1349375
https://bugs.launchpad.net/juniperopenstack/+bug/1349375

Change-Id: I7bdaaf6c071eb87de103d806727d2dd5bd46671f
Merge "raising proper exception for invalid allocation-pool and modifying display message for out of cidr gateway ip. This will fix 1349375 https://bugs.launchpad.net/juniperopenstack/+bug/1349375" into R1.10