Merge pull request #4 from mbedmicro/master

Sync with master
Host test refactoring: cleaned a bit functionality of host tests. Forced test() function in DefaultTest to be method returning test result
Cleaned pyFlakes issues with unused imports
Minor style improvement
Merge pull request #588 from PrzemekWirkus/host_test_OO_refactoring_part2

Host test refactoring  - part2