System.out.println -> Logging

Closes #715: Replaced all System.out.println() with proper logging
more refactoring in reef-io (logging, code style, minor fixes) - not finished yet
more refactoring in reef-io (still not finished)
Merge branch 'master' of github.com:Microsoft-CISL/REEF into weimer_715
Merge branch 'master' of github.com:Microsoft-CISL/REEF into weimer_715
Merge branch 'master' of github.com:Microsoft-CISL/REEF into weimer_715
Merge branch 'master' into weimer_715
minor fixes in AllReduceManager
more refactoring and cleanup in ReduceHandler. no functionality changes
remove unused nsPort variable in NetworkService constructor
Merge pull request #716 from Microsoft-CISL/weimer_715

The reported test failure is immaterial for these changes. Merging.