Support numerical protocol value for RuleProtocol

To be compatible with Neutron, support both the numerical and
string values as an input to represent the security group rule's
protocol.

Change-Id: I57c06f1c02972f73ab61272df6443f801e62fa82
Fixes: MNA-21
Merge "Support numerical protocol value for RuleProtocol" into staging/v2014.11