Create global config to specify a list of country codes that should be
excluded from node selection during uploads.
This exclusion is not implemented when the upload selection cache is
disabled.
Change-Id: Ic41e8b4f18857a11045668eac23107da99668a72
This commit doesn't change any behavior, just organize the code in
different way to make it easier to implement different Criterias
to include nodes. Today we use NodeID and Subnet based selection
but later Criteria can be extended with different kind of
placement rules (like geofencing).
The change nodeselection is used by segment allocaton (upload) and repair
and excludes nodes from an in-memory selection.
Resolves https://github.com/storj/storj/issues/4240
Change-Id: I0c1955fe16a045e3b76d7e50b2e1f4575a7ff095
