translator: make edgelb pool name optional

[bmcustodio]

This PR makes the kubernetes.dcos.io/edgelb-pool-name annotation optional. In case a value isn't provided, dklb computes the name of the target EdgeLB pool according to the following format:

<mke-cluster-name>--<namespace>--<name>

where <mke-cluster-name> is obtained from the MKE cluster's name by replacing all forward slashes with --. This means that, for example, if the MKE cluster's name is dev/kubernetes01, the EdgeLB pool for the my-svc service in the my-namespace namespace will be

dev--kubernetes01--my-namespace--my-svc

The -- separator is not ideal, but it is pretty much the only option we have given the limitations on the name of an EdgeLB Pool:

# dcos edgelb create pool.json
{
  "code": 400,
  "message": "pool.name: foo:bar invalid: did not match ^[a-z0-9]([a-z0-9-]*[a-z0-9])?$"
}
dcos-edgelb: error: [POST /v2/pools][400] V2CreatePool default  &{Code:400 Message:pool.name: foo:bar invalid: did not match ^[a-z0-9]([a-z0-9-]*[a-z0-9])?$}, try --help

[pires]

LGTM