* fix cv::imwrite to allow cv::UMat and vectors of it to be written

* cv::imwrite failure handling improvements

* Unit test for regression testing imwrite support for and fix whitespace

CPATH entries are processed before any -isystem:
https://gcc.gnu.org/onlinedocs/cpp/Environment-Variables.html

- disable "-Wsuggest-override" in tests

* Solves #11156

* Check file size for all file format. Disable APPEND if file is empty

* Add test for APPEND mode