Use correct version of ubi config file for ubi repository population

[rbikar]

Summary

In order to support new branching scheme for ubi config repos, we need to reflect that also in ubipop. In short, ubipop should select correct ubi config file based on version for given repo.
There are two scenarios for different types of repos:
For DOT repositories:

• select ubi config by platform_full_version repo note

For mainline (e.g. 7Server) repositories

• select ubi config by ubi_config_version note
• if repo note is not available, use default version ("7" for ubi7, "8" for ubi8 )

I both scenarios, if a config is not available for given version, fallback to default version.
Version of ubi config will available via version attr - release-engineering/ubi-config#49

Issue Type

• Feature Request

Current behavior

Currently we don't support selecting ubi config file per version.

Desired behavior

• for every ubi repository correct ubi config is select by its version
• for determining which version should be used take platform_full_version repo note for DOT repositories and ubi_config_version repo note for mainline repositories
• if ubi config is not available for given version, fallback to default version ("7" for ubi7, "8" for ubi8 )

Use case

Ubi DOT repositories are considered as testing repos, so we may want to used different (new) config file for for DOT repositories than for mainline repositories which are customer facing.