The Compute API requires 'from_port' and 'to_port' to be -1 for
ICMP security group rules. It happily accepts them empty or None
but the resulting rules do not work. So we force the values for
ICMP rules.
Closes-bug: #1477629
Change-Id: Iba57211014caca16be7c9a28d15d4db2a6c51b8d