* Fix bug introduced by #2238

* Added a debug logging macro: NGRAPH_DIST_DEBUG which prints the timestamp and MPI rank for distributed AllReduceops

* Fix bug introduced by #2238 on r0.15 (#2515)

* Fix bug introduced by #2238

* style

* Fixed code formatting.

* Moved the logging implementation to log.cpp

* Fixed clang warning

* Don't use namespace in header

* Fix ifdef

* disable warning

* Fixed Centos build issues (gcc 4.8.5 doesn't implement std::put_time - hence the issue). Also fixed a logical error in the distributed setup for unit tests