MAAS only accepts CIDR IPs that do not have host bits set otherwise
MAAS sees the CIDR as a second network. This commit adds a Drydock
validation that checks if the CIDR has host bits and also suggests
which CIDR to use if the provided one is not acceptable to MAAS.
Change-Id: Ib6d4d8277d0e1634524426a08e138e39fb37f14b
fdb6dcaca6