Fix resolution of getHubHost and getHubPort in GridNodeConfiguration.

[kool79]

There are several related issues:

issue 1:

As documented here the hub parameter should take precedence over -hubHost and -hubPort.
But actually parameter -hubHost and -hubPort have higher priority when both params defined.

issue 2:

When one of the hubHost or hubPort is equal to null then result returned by getHubPort() and getHubHost() can depend on invocation order:

Precondition:

hub: "http://hostA:1111"
hubHost: "hostB"
hubPort: null

step 1: call to getHubHost() returns "hostB" (from hubHost parameter)
step 2: call to getHubPort() returns 1111 (from hub parameter)
step 3: repeat call to getHubHost() - now it returns "hostA" (from hub parameter)