Add randomization in the gateway selection process

[emmdim]

The current implementation of gateway selection orders the gateways based on the health metric provided by the getGatewayInfo request.

One possible approach of randomization mentioned by @p4u is assigning random weights to the gateways and sort them according to some functions such as:

h_i : Health of gateway i
w_i : Random weight of gateway i in (0,100]
preference_i =  h_i * 0.6 +  w_i * 0.4