* Caching support of multi-device scenario
- IE_CORE: introduce CacheGuard which can create locks for specific cache identified by 'hash'
- Added functional tests for it
Fixes of Thread Sanitizer failures:
- ngraph::Serialize - m_ref[i] can create new element, casted to 'const' to avoid this
- ngraph::get_opset oprations: reworked to use std::call_once instead of double bool check
* Added docs for ie_cache_guard.hpp
* Fix Debian 9 compilation issue
* Fix build for CentOS 6
Added assert to verify that table of locked hashes is empty on destruction
* Fixed review comments