Merge pull request #317 from euroelessar/lts

tests: Fixed path to cocaine runtime
Merge pull request #318 from euroelessar/lts

tests: Write artifacts to source directory
Merge pull request #319 from euroelessar/lts

srw: Don't call cocaine::app_t::stop on stopped apps
Python: Fixed rebase conflicts.
Merge pull request #321 from shaitan/lts

Python: Fixed rebase conflicts.
Monitor: Added ability to extend monitor statistics via custom statistics providers.
Merge pull request #322 from shaitan/lts

Monitor: Added ability to extend monitor statistics via custom statistics providers.
tests: set stdout to sys.stdout instead of PIPE

It makes better user experience as tests' progress is printing
in real time
prepare_latest fix

In case if one of prepare_latest's groups is not presented in
state's list prepare_latest throws an exception. This fix adds try
catch statement to catch the exception and returns appropriate
error code