better Travis integration

- removed Yast stubs, install real Yast instead
- run all tests at Travis
spec_helper.rb - force loading all Ruby files

to report proper code coverage
switch to SVG badges
code style fix - use do/end for multiline blocks
use `rake test:unit` for running tests at Travis
better load all files in tests
Merge pull request #175 from yast/Travis

Better Travis support