Cover 'Critical' and 'High' bugs via the set of tests and checks

'Critical' and 'High' bugs should be covered by apropriate tests and checks, to automatically test known regressions.
Due to very different behaviour of the bugs, there will be several groups:
- Tests for Fuel admin node;
- Checks for data prepared by Fuel for slaves before and after deploy (validate configuration parameters and system settings on slaves)
- Tests for individual components of a cluster after successful/unsuccessful deploy to get actual (functional) status of components in the deployed/failed cluster. This will help to quick investigate why the cluster failed or what components are working not as expected. Most of test cases should be implemented in this blueprint: https://blueprints.launchpad.net/fuel/+spec/fuel-library-modular-testing
- Checks for particular key phrases in logs in case if there is not possible to get actual status regarding the issue from a component. This will cover 'hidden' bugs that usualy not appeared in functional testing directly, but can be found in logs by key phrases.

QA: Dennis Dmitriev, Maksym Strukov